What if the block fails a sonic test on a stock stroke rebuild? Is assembly cost free on a stock stroke rebuild? Are the bolt-ons and gears free? Is the labor on rebuilding the rear-end free? How much more cost is there in inspections on a stroker than a "good performance rebuild?" Your comparison is taking into account all the costs that a 496 build would have, but not the costs that a professional stock-stroke rebuild would have.
Having re-read the OP's posts a few times, I do admit that I might have misinterpreted them. It looks like he doesn't want to pull the engine and does want to keep his bottom end intact, just swapping heads, cams, intakes and exhaust. But he's also seemed to indicate he wants to keep his rear-end the same. Will a revvier 383 be very "snappy" with 2.76 gears? A slab Fury isn't very heavy, but it's no E-body either.
I admit, I'm biased heavily towards torque, but that's because I have a 5,000 lb Imperial and not a 3800-lb Fury.
So, to reset as what I would do keeping the engine in the car, and the bottom-end intact, and willing to rebuild/port heads, upgrade cams and exhausts, I would go with 440-source or Edelbrock heads, mild cam (aftermarket under 200 degrees of duration at 0.050" at least 112 degree LSA), new aluminum intake, and maybe exhaust depending on what his dual exhaust is now. If we're talking about gears, I'd go with 3.23 and could live with more duration (like 225 degrees).
OK, new we are getting somewhere.
I did just talk with Dan. He is looking to make the car a dependable cruiser and have a little more pedal power. He would like to see 400HP, but this may be a little high for a street car & driver combo as it may fall more into the street/strip realm and no be so much a comfortable cruising car you can drive an hour away to a car show. I think 350-375HP would be a better goal?
Dan lives in Colorado which is at a higher elevation so certain components need to be taken into consideration, ie compression.
The block is .040" over, so it has indeed been rebuilt at some point. Flat top pistons. Heads are the "906" type - which I read are "open chamber" heads. Seems closed chamber are preferred by the race/HP guys, but open chamber heads have their advantage.
Dan is now looking at keeping the short block as is and making improvements to the "906" heads, but first will have a machine shop look them over. This would include Dan doing some basic port/gasket matching and cleaning up any casting lines or bumps in the intake ports to smooth them out -nothing more. A three angle valve job. His valves may be good enough to do this, but I would install new stainless steel valves, bronze bushings, new springs to match the cam. Hardened exhaust seats? I feel SS valves don't need them, but others will differ on this. This is option #1 on the heads.
Option #2 was possibly upgrading to the "Stealth" heads. Not a Mopar guy, I had to read up on these. The description states they are a reproduction of the stock "906" head. They can support up to 650-700 HP with work. Price looks to be good for an assembled head @ $499.95 each, or $1,000 for the pair. Says they can be painted and look lie factory. Stealth Aluminum Cylinder Head - COMPLETE - SINGLE HEAD-440 Source
Rebuilding the iron "906" heads may come in a little cheaper than the Stealth heads, BUT, what are your opinions on this, Iron "906" refurb or "Stealth" heads? Keep in mind that aluminum heads draw more heat and typically require another point in compression to compensate. Would Dan's flat tops work at his higher altitude along with the Stealth heads or would the iron heads actually be better in this situation?
Next is the intake. Dan likes the "stock" look and would like to keep the factory 4-Bbl piece. His carb is a 600CFM AFB. My suggestion is to go a bit bigger on the carb like a 750CFM which has the vacuum ( or weighted) secondary air valve. I actually recommended a GM Quadrajet in place of the Mopar version - the Thermoquad. Plymouth actually used the Q-jet on some of their police package cars. I like the small primary bores for better gas mileage and keeping up intake airflow and then the bigger vacuum operated secondaries for more flow/HP. They also have their own unique sound. Don't know if a 750 AFB/AVS would fit on his 4 Bbl manifold without opening up the rear holes larger to match the larger bores of the carb? It would require a spacer/adapter to use the Q-jet/Thermoquad and linkage adapter for the Q-jet, or might a 400CI which had the Thermoquad work and still have the "look" of his intake?
Car already has dual exhaust.
Cam selection. I recommended Hughes Engines for a cam. Reason is that they understand "cylinder pressure" which is very important in matching the cam to the compression ratio. You can get a great grind that will really work with low compression engines. Typically, iron headed engines should be kept in the 9.0 - 9.3 to 1 range if running pump gas & no additives. This changes when at altitude as more compression is needed, ie "cylinder pressure." You can find an article on this at Hughes, but here is their main page: Hughes Engines
Here is another great write-up on cams and cylinder pressure. These guys have some great videos which I have purchased. Great info if you want to learn - its Chevy biased, but the principals are still the same: How do cams affect compression?
At this point, a torque converter upgrade will be made. I base this on my own '73 Fury with 360CI and factory 2500 stall converter and 2.76 gearing. It is a "loose" converter and takes a little pedal pressure to get the car rolling if easing into the throttle. Slap it down and it takes off rather fast for a big old boat. I installed a "tight" 2500 RPM converter in my brother's 360CI, modded 904 trans, and 3.55's out back. The gearing no doubt helps, but the converter does not slip like my factory converter. On light throttle, from applying the gas to letting off, it drops 200 RPM's. Nail it from a dead stop and it does as it should and lights the tires up. Here is where I got it and will get one for my car when the time comes. They have a from to fill out and I talked with the owner who personally took all my info: Mild Street Edge Converter for Chrysler 727 Transmissions [MSE727] - $345.00 : Edge Racing Converters, More Horsepower with More Torque Guaranteed!
A swap to a set of 3.23 gears may be done in the future, but the converter was going to be added and see how the car responded. I would also suggest a "shift improver kit" to firm up the shifts of the gears as this can aide in picking up a little more "free" performance.
That is where it stands right now. Could all change tomorrow, nothing is ever carved in stone when building an engine and it isn't over until you hit the key to fire it up.
So input is welcomed as Dan is still gathering info before committing to anything on his build.