I once converted a 16cc to a 21. If one searched hard enough, you might even find comments about it here in the forum. I had to do something about a mismatch with the wrist pin, but I just can't remember now what it was. If I have time later I'll try to research it here in the forum for my old posts. But anyway, it worked!! (At the time I was trying to come up with something lightweight to use on .60 size planes, and the 3 bolt 16cc crankcase was lighter....)

AV8TOR