The R4 P5 stuff is way cool,but you cant go real big on the cubes because the block..and those engines are way hard to find..

Here is a good run down on a very high HP small block,with wedge head...

R3 block
60mm cam almost a inch lift
420 to 440 cubic inch
very light weight crank aka,LA enterprise,winberg,etc
GRP rods,
custom Diamond pistons
A double throw down set of W8 10 to 13 degree CFE heads.
CFE sheetmatal manifold
dual 4500 dominators
external single stage peterson oil pump with star vacuum pump.

I think you could make 1050 to 1075hp..yes with a wedge head!!

I also think you could get 1000hp with cast manifold,single four at 420 to 440 inch also