The engine was rebuilt years ago. It's running fine just the valve springs getting weak. I know the guides had to be machined for the dual spring setup. It has a Hughes engine retro fit roller cam setup. I was looking for the valve guide size to order the correct valve stem seals. I may have to wait until I get there and measure them. As far as I can remember it's the stock size valve guides in there. I'm not looking to change them.