I had a short block rebuilt along with heads for my 62 Impala. It is a 66 motor, 275HP, and I am nearing installation. I wrote down all the casting numbers and date codes for future reference. On the back of the block this series of letters is part of the casting: CONV1. The number may be the letter I or L. The block is 3858180, J75. Just for educational purposes, does anybody know what the CONV means? Anybody?