Hello Again, The bit test showed the 17/64 bit was tight in the end areas. The center plug area is raised. So this is a 390 way overbore at the factory, then bore to 4.130 because they had no pistons? or a way overbore 352 to be a 428 block? Curious. Or they goofed like I thought. Don't know anymore. Thanks for the insights. Have a good day Phil