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IF these pistons were in the engine when it was running, the engine must already be bored 30 over. Right?
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Maybe. It'd be best to measure the bore. At least, put a piston in and check clearances with a feeler guage for an idea of size, though it can vary with wear and you won't know whether its the piston that's worn, or the bore, or both....
If you've a machine shop doing the work they should check that all (Bore size, roundness, etc.) out as routine....