OK, I did some "REALLY ROUGH MATH" and switching to a set of closed chamber heads and if you used a .020" head gasket you would bump your static compression up approximately one point. This is based on if your heads are 83 cc's now and the replacement heads are 73 cc's.
We dont know where your piston is @ TDC. By that I mean is it at zero deck or is it way down in the hole. If for some reason it's close to the top of the deck then you will gain some power from the quench area of the head.
Basicly what I'm saying is that its really hard to say what you would gain from doing these mods but you have a good platform to begin with. The 400 has the largest cylinder bore of all the big block engines so it responds well to things such as oversize intake and exhaust valves.
Also keep in mind that you dont want to get too caught up in the big compression game. Yes a bump in compression will usually make more power but keep in mind that you live in the desert and tuning and cooling will be a big factor.
Ted
