440 swap or build the 383?

I would have a question for you, and then suggestion on how to reach your goals:

Old guys like me that reached driving age in the malaise area of the 70s have a point of reference for
“ performance” that is wildly different for younger people from the computer/fuel injection generation.
A well tuned 383 roadrunner is a strong running car to someone like me yet my current daily driver turbo gas VW wagon (that gets 38mpg) would run neck and neck with that old Mopar. My point is if your point of reference of a fast car is something like a current coyote mustang/392 Challenger pretty much anything you do to “hop up” The old Polara is going to leave you disappointed.

Here’s a suggestion: before you start changing anything find a Way to drive or ride in a proper running/tuned old Mopar. A restored stock 383HP would be great on one end at the spectrum and then try on a worked over 440.
Honestly, you may be seriously disappointed with both, and that will answer your question whether to even spin a wrench at all under the hood of that old Polara. If you find you enjoy the experience comparing the two, stock 383HP (which you could easily duplicate for minimal cost) or a complete modified new build, Could be a fun future for you and your 65.

Steve weim55 Colorado
I’m 48, but I’m not trying to make the car run up on Hellcats or anything like that. I just want a fun torquey cruiser that can boil the tires. Honestly the car is great as-is, I just can’t leave anything alone and I want more out of it. I have an LS swapped Jeep that suits my ‘modern’ speed itch. I’ve been basically a motorcycle guy for the last 30 years and just starting to get into cars heavily. I’ve always liked them and wanted to do one but space/time/money was an issue back then. Everything I have other than my daily is either motor swapped or at least has a cam and headwork. The workshop part of it is more fun to me than the driving.
If your 383 is not using oil/blow by I would do a cam swap. Those early 60s cams are pretty lame. If you have the 284/484 cam well you own it, but you can do much better. I personally dislike that 284/484, the 292/509 cam is waaaaay better. The stealth heads will bolt on and put you approximately same compression as cast iron #516 heads on your car, but breathe better. That stock 4 bbl intake is not that good and exhaust manifolds are crap. So air in air out and you will make more power. 440 is a crap shoot, low compression is Dyno ok, but they suck on the road/track, so I would not go that route, plus they want a arm and leg plus your first born for some junk they pulled out from a fishing pond
A 400 ci or 440 stroked I don't think makes any difference for a big old Chrysler on the street on pump gas, it just matters what is easily available and cheaper. You could stroke the 383 up to a 496 but know nothing about it.

Some bathroom reading.

I will do some more pontificating, because of above mentioned strokers.
Yes the 400 block is desirable because the bulkheads are thicker above the main bearings. Until you get upwards of 700 hp range this means very little.
The 400 and 440 are desirable when striving for these kind of numbers because bore size equals more airflow or bore is not as close to valves so more air can move into the cylinder.
If you only have 4.25" and the valves (side by side) add up to around 4" + gap between you start to get close the the cylinder wall. This makes the air turn again and hampers flow.
All of this is for big power and getting to higher rpm.
The 400/440 will take a overbore to accept a 4.375 piston which is a very common piston size that fits in many stock blocks.
Strokers are nice, but if your only going to put a medium hydraulic flat tappet cam in it, what did you gain? Hey, if you want to strive for 650-700 from a stroked 383 go for it, your not making that with a hydraulic flat tappet.
This is why I suggested just a cam swap and intake and exhaust. Plus everything is reusable on a stroker. The intake would not switch to a 440, but you could skip it if your still not sure you may go that route.