Howdy and welcome!
By '68, the 383 2bbl was really a low compression 4bbl motor. Heads should have the larger 1.74" exhaust valves. The cam is the 256/260 cam that was the 4bbl cam for many years, as the prior 2bbl cam was the 252/252 .390" lift cam. So, in that respect, all you really need to be at the '68 383 4bbl specs, other than the higher compression ratio, is the 4bbl, intake manifold, and dual exhaust system.
Ignition upgrade, hard to go wrong with the Chrysler Mopar Perf electronic ignition kit, just use a normal non-Orange control box. It's already got the fast advance curve in it. Easy to install, too. You can add an MSD box to it, too. AND if it matters, it looks totally stock, like the factory electronic ignition did in '72 and later.
Surface and clean-up the ports in the heads. Gasket-match the intake ports, clean the burrs and such from the ports, etc. Nothing special. Same on the exhaust side. It's possible that the guides will have some wear on them, especially #7. Do the bronze helicoil guide upgrade and then the wear interface will be the bronze helicoil, which can be replaced later on. A quality chrome stem undercut head valve should work very well. Pretty simple and easy to do. Use the FACTORY-style valve guide oil seals, or upgrade to the orange silicone versions (big block Chevy, as I recall, then trim them to length).
Intake manifold? Probably the Edelbrock dual plane for the 383. Might even still have a Chrysler part number on it! That factory part number, cast into it, made it "stock" in the eyes of NHRA as a "stock part", so it was legal in the stock drag race classes . . . and better than the factory cast iron item.
Carb? The factory 4bbl carb would have been either a Carter AFB or Holley 4160, either one about 550-600 cfm. The Edelbrock AVS-2 650 cfm would be a good choice, I believe, or the Street Demon 650 cfm carb. The AVS-2 has been on sale at Summit Racing for the last few weeks.
The self-learning EFI is a neat deal to do, IF you want to spend the money. For my orientation, a well-tuned carb is almost as good as EFI in performance. The EFI might have a little sharper throttle response, maybe even a little increase in mpg, BUT it's still a "fuel/air mixer". Analog or electronic? Your judgment call.
Bearings and rings? Bearings need to be at least "OEM-level quality" in material. Some of the factory 4bbl bearings were "Tri-Metal" rather than just normal babbit. Rings? Same at least "OEM-level quality". Many of the 4bbls used Chrome-Moly compression rings up into the middle '70s. These rings will need a slicker/smoother surface to work against than regular rings might, which means a finer grit final finish hone on the cylinders.
Pistons? This can be a little problematic as the pistons I've found in online catalogs are typically the lower-compression versions, flat top, which fit 2bbl and 4bbl from about '60-'71 model years. Use the casting number and compression of your existing 9.2 CR 2bbl pistons as a guide to ensure you don't end up with something lower than 9.0 CR. The OTHER determiner of CR is the head gasket thickness. Most of the stock steel shim gaskets, back then, were about .020" thick, but the composition gaskets now available are more like .045"-.060" thick, which can lower the CR by about .5 point. So get all of this figures out with your machine shop BEFORE you purchase pistons. There are some formulas to figure CR. You'll also need to know the actual "cc" of the combustion chamber volume on the heads you'll use, too.
On the intake manifold/valley pan gasket, IF you decide to upgrade to some of the Edelbrock aluminum heads, there's a gasket kit used on 440 6-pack motors ONLY which consists of two pair of paper gaskets. Maybe two kits of 2 gaskets each? The purpose of these gaskets is to provide an interface to keep the metal from the valley pan gasket from eating into the aluminum of the intake manifold and compromising the sealing surface in the process. Cast iron heads? Just use one pair on the aluminum intake manifold side.
Now, I've left the cam selection to toward the end. ONE reason is that unless the car had the optional 3.23 rear axle ratio, it's got a very highway-friendly 2.76 ratio, which with the 8.55x14 (original) tire size, means it's running about 27.6mph/1000rpm on the highway. THEREFORE, too much cam will decrease low-speed performance and response. With the 3.23 ratio, it makes just over 25mph/1000rpm. Either way, adjust the trans kickdown linkage so the trans upshifts into 3rd gear right at 28mph (2.76 ratio) or 25mph (3.23 ratio). What this does is keep the light throttle upshift to not happen too soon, resulting in all acceleration past that point "on the converter" rather than "by gears" (which is more efficient and raises the other part-throttle upshift speeds just a bit for more acceleration with less throttle). You can also upgrade the TF to part-throttle upshift with '71 model year parts, just change the appropriate parts.
Lunati has several interesting cams.
The first one is their "Factory Perf" . . . 216/226 degrees @.050" lift duration, .455/.475 lift, 112 LSA, 1800-5500 stated rpm range
The others are VooDoo roller cams with clost to .500" lift and would probably work best with roller-tip rocker arms. Similar duration to the Factory Perf cam.
The KEY is not to get too much cam for a car driven on the street, especially one with a highway rear axle ratio.
To help things along, you can use the "Road Runner" torque converter, which crosses with the Slant Six, converter, for a little higher stall speed than what you now have.
Exhaust? You can opt for the '69+ HP cast iron manifolds and then use 2.25" or 2.50" pipes with them. There are slight variations between each model year, which can be the way the pipe flange is clocked on the manifold. Or you can use headers with quality gaskets.
I suspect you just want a better-running 383, so start with the 4bbl intake /carb change, then the exhaust and ignition upgrades. Then you can do the camshaft upgrades later, if desired.
In watching the many online dyno runs, other than "Nick's Garage", many of those builds are too radical for something with a 2.76 or 3.23 rear axle ratio. The carbs might not be fully-dialed-in for a daily driver street car that needs to get good fuel economy AND are usually too big to do that. Makes for good dyno numbers, though. The larger-runner aftermarket heads might build more power, but that dyno pull will not evaluate off-idle or part-throttle throttle response as they are done at WOT. If you're staging at 2500rpm for a rolling start, THEN it works.
Sorry for the length. LOTS of things to cover and consider.
In machining the block, get the main bearing saddles "line honed", then the rest of the machining operations will reference off of that. The Sunnen CK-10 used to be the alleged "industry standard", but Rottler and others have similar machines. Do all boring and final hone operations with deck plates AND inquire as to how well the operator knows how to read the load meter when doing the power hone operations. If too much time is spent at one part of the bore, it can result in a non-straight cylinder surface . . . a reverse "hour glass" type shape.
Be more concerned with how the car will drive on the street RATHER than worrying about how much horsepower it'll make. That max horsepower only happens at elevated rpm levels, it's "torque" that moves the car from idle upward. You might have a 450 horsepower motor that won't scatter crap from a red light at part throttle, for example. Everything HAS to work together, which is what made Chrysler's engines so great. The combinations all worked well together and were well-executed at the factory level. In many respects, you could do a lot worse than to mirror the factory 383/335 engine's specs, including the stated torque converter.
CBODY67
