You may be surprised what you find thick walls in. I’ve got several 318 blocks that the core revision number is -3. One is a 1973 block out of a 3/4 ton automatic truck with a large B cast in the outside, another is out of a ‘75 half ton, and another is an ‘82 reman by jasper from a truck. All of them are thicker between the cylinders than a 1990 industrial 318 hydraulic roller block I have and also have blind head bolt holes. The late 318 block would take a 4.04 inch bore, no sweat. I could spend a week straight sonic testing this stuff and posting the findings here.
