Those are just standard 8.5:1 250 cast pistons, correct?

These would be a little bit better ones to get to bump up the compression a bit.
http://www.ebay.com/itm/307-CHEVY-PISTON...870&vxp=mtr

Flat tops, w/4 valve reliefs.

Or these, if pic is correct. http://www.ebay.com/itm/Federal-Mogul-TR...39f&vxp=mtr

MBHD

12 port SDS EFI