I am rebuilding a Gran Coupe 383 2bbl car, it came with two 383s (one original). It has a 727 trans and 8-3/4 rear.

In my head I'm thinking warmed up 383 with F.I. for reliability and a 500hp target, mostly to avoid significant investment in the rest of the drivetrain.

Is 500hp range a reasonable expectation? I've heard it's hard to get more than 1hp/ci from a 383 Mopar motor, and I suspect it may need to be a lot bigger.

Also I've built a few LS1/2/3, flatheads and small block chevys, but haven't built a Mopar. Is there a good shortblock builder in the SF Bay area (to use the numbers matching motor), or a recommended vendor for the motor and trans?

The more cubes you have the better off you will be. Torque is king! My choice would be to build a 400 stroker, either 499 or 512 cubes. That is built using a 400 block and either a 4.15 stroke crank or a 4.25 stroke crank and 4.375 bore. 440 SOURCE has a lot of info that will help you understand what you are getting into. The big deal with strokers is they make so much torque down low you can build a 499 that will be a blast to drive and you can use 3.55 or even 3.23 gears, a mild cam, and a tight converter that feels like stock till you stand on it.
If you need to budget then go for big cubes and use a mild rate of lift cam that won't kill the stock pushrods and rockers. Older cam designs designed for chevs can do this and still make decent power.
There are also 383 stroker kits available from 440source. But keep in mind 383 blocks are weaker than 400 or 440 blocks. Don't be afraid to build a bb mopar. They are very simple and straight forward. Just aquire books and good measuring tools to check everything.

My first recommendation:
1) Buy aftermarket aluminum heads rather than put money into the stock 383 iron heads. There are low cost versions that will make more power than the stock heads.
My second recommendation:
2) Buy aftermarket connecting rods. There are reasonably priced H-beam (or even I-beam) rods that will be stronger.

Check out Marsh Performance and 440Source, etc.
Link to Marsh Performance

500hp from a “warmed over” 383 ain’t gonna happen.

383’s that make the type of HP are fairly high strung........ and need the necessary support pieces(converter and gears) to have good performance in the vehicle.

Put a 4.25” crank in it...... then you’ll be closer to the 500hp goal with the “warmed over” type of build.

Yea.
0.030" overbore to 4.28" will give 489 CID
0.060" overbore to 4.31" will give 496 CID

For your goal, I would leave some more metal in the cylinders and bore +0.030" to 4.28"

I'm sure there are plenty of good engine shops in the NorCal area, not sure about SF itself but you'll be able to find someone in the region.

I agree with the 4.25 crank route. Put a 4.25 crank in it, use pistons that give you 9.5 compression with the heads you pick and go with a modest camshaft that matches how you are going to drive the car. I'd use Trick Flow 240 heads on an engine like that but Edelbrocks or Stealth heads can also be made to work. Keep the header size on the small size and use a Holly Sniper with a Hyperspark distributor setup. You should be able to make 500+ hp and 500+ torque and have a smooth idle, no bucking at low speed and gobs of power for passing or on ramp blasts. You won't need a ton of gear out back either, 3.55 gears will probably be enough with the long stroke.

1.20-1.25 ft/lb per ci shouldn’t be much of a problem, even with pretty tame combos.

That’ll put you in the 580-600ft/lb range @489”.

From the 440Source.com web site, a 78cc Trickflow 240 heads will result in a compression ratio around 10.3.
With the aluminum heads and moderate cam, I think that will run just fine on pump premium gas.

OP lives in CA which has terrible gas. 10.3 might be okay, he'll need to discuss it with his engine builder. Diamond has a 24 cc dish piston for the low deck 4.250 combo so if I was building the engine I'd probably lean that way. Just to make it as fool proof as possible even if it gave up a bit of power.

My first low deck pump gas stroker motor was a 400 block bored to 4.375 bore size with a 4.250 stroker crank in it. I had a set of iron 906 heads on it with big valves, 2.14 intakes with 1.81 exhaust mildly ported and polished, they flow a little better than a well prep set of NHRA legal stock set
I had a low deck six pack intake on it with a set of stock type 1970 Holley 440 six pack carbs set up well, that motor made 612 HP @5500 RPM and 644 Ft. Lbs. torque at 4500 RPM with 9.25 to 1 comp. ratio using CA pump swill back in 2002
A single four barrel carb with a decent aluminum dual plane intake might loose 10 to 20 HP depending on the size of the carb and how well it is tuned to the motor and the intake that is on it. On your deal with a little less C.I. you might struggle to make 560 to 590 HP with 600+ Ft. torque, still way more than you have now
If I was in your seat I would put a set of the Trick Flow 240 heads and a Eddy Performer RPM intake with a carb you like and go have fun spinning the tires off that rascal

Lots of great advice here, thank you for keeping me on the right path!

I was worried the recommended route was to go all modern.

We have done a ton of 400 and 440 strokers using 440Source....Great parts, great prices, and they all fit well. No complaints. For a 383, you can go to 496 and then as mentioned, put a fair set of aluminum heads on it.

We like the Indy EZ heads, and have made darn near 800hp with a set on a 400 stroker....Just an awesome combo. Don't skimp on the rockers or the pushrods though. The low decks have more angle than a 440 and really need a rocker that centers well in the hole....We used the Comp steel ones, and they are awesome.

if I had to have 500hp from a 383 i'd pro-charge it. 500hp from a 383 with big cams, FI, big crank, big heads, etc just sounds miserable to me. a real 360hp-380hp for a pump gas driver would be fun; done this before. a warmed up pump gas/license plate, reliable, easy maintenance 400-420hp 431 would be more fun. blowing a bunch of money for the more exotic build and just plain enjoyable fun aren't always on the same page. low gears and loose torque converters are miserable. another thing; can you tune the more radical build? how dip can the money pit be dug before you begin to regret it?

I can make nearly 750hp on a stroked 383/496 for less than the price of the Procharger!

and then the next guy says he can make 1000hp; to what end? worthless money pit?

To get 500hp from an aluminum headed 489...... that would be a very mild user friendly combo.

Pump gas, HFT cam, no problem for power brakes, occasional DD use.

Never have to take it over 5500rpm.

Same type of build and hp/ci as a 450hp 440, or a 390hp 383.

My point was you do not need a procharger . The 383 is very capable of attaining the goal without it...Prochargers are neither cheap or nor super easy to tune....

Me thinks any type of boost will be the wrong way to go on any stock OEM production 383 block due to the thin main webbing like all the stock 440 have blocks are. That is a hand grenade with the pin pulled waiting to go off into detonation on a hot summer day at WOT
The lower compression larger C.I. stroker motor makes a lot more since to me