I took the heads off a 64 (11-20-63) dated 273 I had collecting dust and found the pistons are pretty high in the bores for a 2bbl design. Flat tops with 4 reliefs 2bbl style BUT they are only .022 in the hole? I measured them with a feeler gauge under a straight edge, .022! Markings are V273 12 7 on the pad and the pistons have a circular pattern on top. I was actually thinking this was an unmolested survivor but it had a felpro .040 head gasket instead of the thin steely so someone was in there at one time. Also there is NO ridge in the bores and no numbers on the piston tops. bore measured 3.629 ish, (maybe the ridge that was removed), but def not a +.010. They also had early 2465315 closed chamber heads so Im wondering what CR these were at.