It is not an ideal situation, I would not build a motor around mismatched cases, but for a guy on a budget, or a guy trying to get through through the season then it will work. The tolerances on these piles of shit are pathetic at best so in the grand scheme of things it doesn't make much difference. I have ran mismatched bore/piston size on twins and triples, ran pistons that one is windowed, one is not so their weights are off, all sort of weird shit just to make the next round or weekend, and never felt any difference or any realistic time changes on the slip...