You really hit the jackpot, my friend - sorry to hear it. It really was a clever and worthy repair attempt. My inner Edwardian Englishman raises his pint to you.
Chances are that it's either the top or bottom end that is damaged, but not likely both. If you were lucky, the pin got snagged in the intake or transfer port(s), and wedged up the piston & cylinder. New top ends are not that expensive - you can just go for it, and buy a 70cc Airsal kit for around $120, if you want.
Pulling off the head & cylinder will pretty much tell the tale. If it's all clean and nice in there, you know whee to look next.
I've got a spare Motobecane 40T engine here, which is also locked up, but might contain some useful parts. I'll try getting it apart in the next few days, and see if anything is useful. Moby engines show up regularly on eBay, and our comrade MoPedLar might also have what you need - he's been a great help in the parts department.