Nah rich. Our motors are not perfectly balanced like the ZO6 ZR1. You can get away with a certain amount of imbalance. If he swapped in another stock piston you would never know. And if you were really careful and the bore was fine you can re-ring the new piston with the old rings and not even hone the cylinder. Not saying its the right way but it is possible.
But yes I doubt he swapped out a piston on his back cause the head would still have to come off along with the oil pan and OMG what a job it would be. It may be possible but I would have to see it.
Wouldn’t have made sense for him to do that since he worked at a dealer at the time so he could have done it on a weekend at a shop. Kinda makes me nervous cause Frank did a trans for me a couple years ago.