Whats the exact bore size?
It probably matches some stock size so its just a case of finding an engine with that bore.
If you have racing pistons with extra narrow rings, easy to find, just use late model bikes as most use 1~1.5mm top and 4~4.5mm oil control.
Just a case of finding manual online (check piston ring grooves for ring width)
This works every time, but, does take some effort
PJ