I don't like the current version of the kb400 piston as well as the original, but I would still use it in an application like this.
The new version has a net zero cc dome. So it's effectively the same as the original flat top, only it has valve pockets so decent sized cams will fit after you've milled the heads enough to get the cr where you want it.

KB400's, block decked so piston is down the hole .015", .027" cometic gaskets, aftermarket heads milled to 78cc, should be mid to upper 9's for compression.