400 big block

452/906/346 all have open chambers, and from what little I've read have similar ports. But, IIRC, most folks opt for the 906s unless they want hardened seats, in which case I believe the 452 is what you'd want. The 516/915 heads have the closed chambers and the 516s sport smaller exhaust valves (1.60" as opposed to most with 1.74"). The 516 also have smaller ports and alledgedly aren't as good a casting-I can't speak to this though. All that being said, I'm sure with good machine work, and some good porting, any of them would make power on a 400 or derivative. 915s are (if I read it correctly) 440 Magnum heads introduced in '67 or '68 and are pretty desirable for high compression in a B/RB engine.

If you google big block mopar heads, there's an article from Mopar Muscle where they did some comparison and work to various heads and reported all the differences...block out about an hour and you'll be able to read through it and view all the charts in there.

I think Diamond makes pistons that would fit that much overbore, and if they don't list them, they can be made. Also, I wanna say JE makes 400 pistons as well.