I have talked to an engine builder (well known) friend, who stated, if i recall correctly, that a number of guys have found that 5.9 used motors had so little wear in them, they would use KB stock bore pistons, no overbore needed. I don't believe that is true with some of the earlier blocks? I will soon get a chance to look at a couple of them , I have a 5.9 Magnum build planned in a couple of months.