First off, "today's safety standards" have nothing to do with what you are proposing. My advice would be to not get in completely over your head (and budget) trying to make a Ferrari out of a Polara. I would basically copy the factory 383 used in the roadrunner - mildly hotter cam (degree'd in), 4bbl intake and carb, some gears and a ~2400/2500 stall torque converter. You should already have pistons rated around 9:1 compression which is fine with today's gas.

Honestly, I know what your post says, but reading between the lines it sounds like you would be more than happy with a warmed 383. The 727 can easily be built to handle 500HP with no issues (you will be nowhere near that) and you should have an 8 3/4 rear which is also bulletproof for your combo. Factory HP exhaust manifolds will work nearly as well as headers at that power level and will be less problematic.