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This is where it gets serious, back at the block. A check with a calibrated finger shows about .005-.007-inch taper in the bores, meaning the block will have to be bored. It's obvious that the engine had been gone through, but had it been bored? Replacement pistons are commonly (but not always) stamped with an oversize number, and we find the "03" stamped on these, indicating a +.030-inch block. A check with a dial caliper at the unworn portion of the bore above the rings confirmed the block was already at 4.070 inches. It's a shame they didn't go .020 inch over in the last build, which is a common overbore size for the 340, leaving +.040 as the next oversize, and possibly +.060 after that. While we surely can go .060 over this time, it would spell the last rebuild for this block. Though aftermarket pistons are commonly available at .060-over, the factory recommends +.040 as the maximum safe overbore. We'll wait and see if the bores will clean up at +.040-inch; it's going to be close.