I've been disassembling my 70 455 engine and I know the heads are from a 68 430 judging by the 1382091 casting numbers. One is Feb 20 (B/20) and the other is April 15 (D/15). What I found weird is in the coolant passages there's more numbers cast inside them?? The D15 head has A in one port and 11 in the other. The B20 head has A in one and 10 in the other. Can anybody tell me what these numbers mean???
