Pete: Overbore in this case indicates your getting 3-1/8" piston versus the 3" factory original. To fit on the same block the sleeve has to be thinner. Your 49 Super A should have block part number 251069, probably R1 or R2, and both 3" and 3-1/8" kits were available. As you get into the newer Super As after serial number 310300 and block part number 354898 R1 it gets a bit confusing as there are 3", 3-1/8" and 3-1/4" bore kits for that one, but they all must be specific to that block. The sleeves that fit block number 251069 will not fit block 354898 or vice versa, the sleeve outside diameter is different. Then one must take into consideration the number of 251069 blocks that have been bored to 354898 specs. How many have ever been done I don't know, I suspect not as many as some might think. It would be cheaper to buy a large bore block, than have the boring done. But who knows why, some folks do funny things. I suspect the folks that have bored these blocks have the know how and the equipment to do it themselves, you start paying for that know how and equipment, it becomes a whole new ball game.
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