The pistons in the 400 are dimensionally the same as good old 351 C pistons, with the exception that the 351's pistons have a smaller piston pin diameter. No problem just have the rods bushed. You could even have floating rods with pin locks for just a little more $$. You can buy dished pistons for the cleveland. They're not cheap, but they are available. Compression will still be high even with the dished pistons. I'd just run 4V open chambered heads. They flow better than closed 4V heads (less shrouding) and they have the same chambers as the standard 400 heads, so detonation won't be a problem. you could even mill the block (or the heads or both) for extra compression. With the right camming and proper intake and exhaust, you would have a 475+ hp motor. Thats no joke. Big problem: custom headers will ruin all the low buck fun. You could run sanderson shorties. Sanderson makes shortie headers for freakin everything check it out.