A good 318 block is casting nr 2536030 with four engine mounting ears om both sides . Up till 1975. I have Sonic tested two sofar and vill bore them to 4.000. then use chevy 327 Rods and pistons .Longer Rods and lighter vristpins. I have 6 more of those blocks to test. I'll comback about vall thickness later. Must work now.