I was surprised that the 983 casting I used on our 321 was thinner than I would have believed. I opened up the intake runner to the size of the alignment ring and broke thru on one of the head bolts. I had to install a sleeve in the head bolt hole to seal the runner.

I also machined a hole in the block so I could measure the thickness of the cylinder wall before we bored the block. It was about the same thickness as a 350 SB Chevy (0.200"). I thought these old engines had a lot more material in them than that. To be safe I filled the block to the bottom of the front water outlet with Hardbloc before it was bored.

Ron