If a hammer had to be used to force jug over piston rings were not aligned right most likely, all it takes is a little pressure around the ring with your fingers as you apply just a small amount of downward pressure on the jug and piston will easily slide into jug.
As far as needing to mic the piston goes I have never seen or heard of anyone coming across a china girl piston that was oversized, I've got them with #2 marked on them #5 marked on them nothing atall marked on them and every single one has always been 46.90mm + up to 47mm for the 66cc pistons never had one that was larger than that, im gonna honestly venture to say that isn't a concern.
Im gonna say all the parts and pieces were just fine and the problem was that installation wasn't done as it should be, I've put an older piston in a new jug with new rings, new piston in older jug with used rings as well as new rings and never had an issue and all the engines ran just fine, the thing that needs to be understood with these engines that have a chrom d bore is that the cylinder wall does very little "seating in", with a light cross hatch hone, the rings actually wear in to the cylinder wall not the opposite, the chrome plating is way harder that the iron rings so the rings conform more to the cylinder than the opposite.
Judging from what I have read here Im set on the fact that this entire issue is an incorrect installation problem not an issue with the components.
If jug doesn't have any deep gouges in it and piston ring grooves aren't damaged, and the little retainer pins aren't driven into piston, this should be an easy fix, but im guessing retainer pins could be damaged now and if jug bore is deeply scratched 3/4" above the very bottom of bore I'd say new jug, piston and rings will be needed and then it needs to be installed right to resolve the problems and get this engine back to at least running condition.