Got the heads off the 360 that was in the 87 RC that the Arizona Chapter boys helped me remove. I know my micrometer is not the best in quality, but I measure 3.98" bore and I thought it was an even 4.0. Do I need another mic? Also, there is no ridge in the piston area. I would think that after 125K miles there would be. So assuming my mic is off, it would mean that either it is only 25K miles (unlikely) or someone has rebuilt this once already?