Another older thread . . .
Back when those motors were built, one reason they might not have put out comparable power as a Chevy was that they were "set up tight for long life". Hot Rod magazine did a build-up on a 1968 383/325 motor. In order to get the power past about 425, no matter what they did, cams, carbs or whatever, it would not make more power . . .until they pulled it apart and clearance the pistons and bearings. So, with normal/decent maintenance, they'll go well past 100K with no issues. Even past 150K.
The stock cam in those motors is the same one that first appeared in the 1958 Sport Fury 350 2-4bbl V-8. Mild by normal standards, with .390 lift and about 252 advertised duration, but it works. Be that as it may.
My experiences have been, on our Chryslers, that by about 80K miles, #7 exhaust valve had "burned" and a valve job was needed. Only did that one head and that one cylinder. So, freshening the valve job might be a decent deal, BUT the old orientation was that when you make the seal "on top" better than the seal "on the bottom", it might cause some issues with blow-by or oil consumption. But, I couldn't tell any big difference on my cars.
I would suggest either the Mopar Perf roller timing set or a Cloyes Plus Roller (I put 400+K miles on one in another motor with no issues). Add the windage tray in the crankcase, too, for good measure.
So, unless there are some noise or oil pressure issues related to crankshaft bearing wear, DON'T mess with that.
For cams, try to find one with 114 degree lobe separation, rather than the common 110 degree lobe separation. I did a 110 degree cam in another engine and I had to play with the advance curve springs to get it better than it was. Intake vacuum will be better with the 114, typically. Most stock cams are on the 114 degree situation.
For the cam "to work", you'll need dual exhausts. The HP manifolds are priced too high for what they are AND usually look like (rusty!!), keeping the stock manifolds might be the best "low cost" option, then getting some 2.25" pipe C-body normal dual mufflers and putting the exits at the rear stock location.
You WILL need the Edelbrock linkage extension item to get the 2bbl throttle linkage to work with the 4bbl carb. You'll probably need to shorten the factory part to get the adjustment right. The kickdown rod adjustment, from the factory, keeps the part-throttle upshift points too low, from my own experiences. From the factory setting (2 turns preload, per service manual instructions, go an additional 2 turns and call it good. No durability issues! It'll accelerate faster with less throttle with the slightly higher upshift speeds. It does make a good difference! With the 2.76 rear axle, it should put it into high gear at about 28mph or so, rather than sooner and making any further acceleration from that lower upshift point "on the converter". With a 3.23 rear axle and the tire size on that car (originally 8.55x14, I believe) it should be right at 25mph.
Adding an electronic ignition might be an option, for good measure. The MP kit is a good one and provides a factory distributor with a faster advance curve in the mix. Just do NOT use the supplied or recommended voltage regulator!!!! PERIOD!!! Using the recommended one kept the voltage at 14+volts all the time. The race manual also notes that it'll negatively affect ALL electrical items on the car, durability wise. I found that out! Went back to the stock unit and had NO problems. Stock or stock replacement ONLY. With the electronic conversion, about the only thing really gained is no point changes, which can be a plus.
Add some iridium spark plugs while you can do that. Set them at about .038" gap and that'll be the last ones you'll need to buy. Adding some magnetic suppression plug wires can be a plus, too.
Stay mild on the cam as the tighter torque converter and highway gears need low end torque to work best. What you'll essentially be doing is putting more rpm into the motor's capabilities without really compromising low rpm performance (which is where we normally drive anyway).
Let us know how it's progressing or has happened.
CBODY67