Probably had probs with the #8 piston because you had a ridge at the top of the cylinder. This is caused by uneven wear in the cylinder by the rings. Any GOOD machine shop should be able to look at your block and tell you if its ok to bore. Standard bore is usually .030 over. You can get a micrometer and measure yours to see if it has already been bored .010 over(marked on piston) or have the machine shop do it. Im speaking with ford experience here, just learning GM. Should all be the same though.