A lot of machinests (old timers) will not bore a motor 'till he has the pistons on hand and will then bore each hole to suit a certain piston (at least the way they used to do it)--only exception I had seen was if you were ordering TRW pistons- the machinests trusted TRW's quality control enough to proceed without having them in hand. I checked a set of six TRWs for a 261 once, and found less than one thousandt inch difference from biggest to smallest piston--not bad!