You're scaring me! My 2002 megablock has one at 0.135" and one at 0.137"! And this is on the thrust surfaces. This is my B1 motor that makes 1060 hp.

Discussed it at length with my builder (Tony Bischoff) and he felt sleeves would not offer any benefit and they are thinner. He recommended filling the block and not looking back. That's what I did.

67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 14.82 @ 94 mph
69 GTX (clone) - build in progress......