I rebulit my 312 originaly in 1969 and bored it .040 over with pistons from my local Ford dealer, or at least thats what I remember. Rebuit it again in 1980 and had to replace one piston. Got it from Ford. Pulled the heads today to go through it again and discovered that the pistons are stamped .0425. Memory fails me on this one. All I can remember is it was .040 over. Depending on the condition of the pistons when I finish disasembling the engine I may want to go with new forged pistons. Am I going to be able to use .040 over forged pistons in the existing bore, or am I going to have to re-bore to .060 over? Checked my Ford parts book and they show the 312 pistons as .020 plus, .030 plus, and .040 plus. 292 pistons are shown as .020, .030, and .040. No plus. Anybody able to shed any light on this mess?