Boss 351 heads were all closed chamber. D2ZE heads were 1972 HO heads and
nothing more than open chamber 4V heads that are set up for adjustable
valvetrain (screw-in studs and guide plates). If you want to run on
pump gas, closed chamber heads are best as they will tolerate a point
more compression ratio for the same octane. If you're running high
octane race gas, that may not matter to you. Open chamber heads may
actually flow a bit better, due to less valve shrouding, but on a stock
stroke engine, the domed piston required to achieve the desired
compression means less efficient combustion.

> I'm flirting with the idea of achieving 500 horse power. With the above
> parts as a basis, I would appreciate any thoughts other Cleveland builders
> might have as to compression, cam profile, & intake selection.

For a 500HP build with high stall automatic, I'd recommend a Holley Strip
Dominator intake manifold. There are also tall race intakes from
Australia. TRW makes (or used to make, they may no longer be available
after the Federal Mogul take-over) a couple of forged domed pistons.
L2408F is designed for open chamber heads only and use the thinner 1/16",
1/16" and 1/8" inch race rings. Compression ratio with 76.2 cc heads would
be around 11.45:1. The L2348F pistons have a smaller dome meant to clear
the tighter closed chamber combustion chambers but they can also be used on
open chamber heads. The L2348F will yield a bit over 10:1 compression with
a 76cc head, about as much as you want to run on pump gas with open chamber
heads. Another way to up the compression is to offset grind the crank to
3.7", run a SBC 6" rod and a custom piston. The longer stroke means a smaller
dome required for the same compression.