I I built my first GMC engine almost 70 years ago. I give them the clearance they called for back when they were built. Those engines were built with almost 90 year old engineering. And they allowed for metal to expand. Back in the day, pistons or valve stems didn't seize when they got hot because they were given clearance. I have known a lot of people wanting to build a quieter engine. They are just not going to be as quiet as a modern engine. We used to say, "they will be plenty quiet after they seize". Here is a manual published in 1958. The top line is the skirt to bore.
