I used to build a lot of GMC heads. As far as I know casting number 2193983 is the only one that fits a 302. They can either have rotating or non rotating valves. We used rotating valves 60 something years ago when we still worked GMC engines. But I see no reason for rotating valves in an engine that is built today. Adjusting them is very critical. I still have the tool to adjust the rotating valves, but I will probably never use it because I just don't see the reason for rotating valves. GMC 302 valves used to be everywhere because the government had so many spare parts for their 302 engines. There may still be some on eBay. I always pressed in cast iron guides and then reamed them to fit. I always reamed them to the maximum clearance number. Most machine shops are afraid to press guides out and back in. They use bronze. But again I would use caution to make sure that they give the stems enough clearance. You must remember that this family of engines was engineered 85 years ago and the 302 was introduced over 70 years ago. And those engines required wider clearances than modern engines. I have seen so many newly built engines fail because they didn't have enough stem clearance. I still have a bunch of valves, but none of them are boxed. I have always just matched like for like
