It’s gonna take more time, and probably money, to fix that top end than to get another.
I know there are piles of stock cylinders, with their resident pistons, sitting on shelves in garages of almost person on this forum. I bet you could get a set for dirt cheap from the B/S.
Get you up and running again and then play with fixing this thing as an experiment. Maybe it could be a backup or you can sacrifice it for porting trials.