Check for core shift. Look at the camshaft hole in the front of the block under the timing cover to see if there is any difference in side to side centering in the casting bosses. Its hard for me to explain, but, easy to see. The front face of the cam bore is machined flat and on that flat surface look to see if the bore hole is centered in the casting. If its way off..1/8 inch or more, then thats .125 off center and could affect the wall thickness of the piston bores making them weaker and then to rebore more meat off makes even thinner cylinder walls. If you don't have much core shift I wouldn't worry . 350 GM blocks are very strong @ .060 over., The 400 blocks are another story because they are already bored .125 from the factory and core shift is extremely critical. Hope this helps. Billy (Racing & Resto)