Thanks guys. Yes, its the 50 CC that's round headed. Looking at them side by side it seems the only difference is the fin size/shape. The plug really stands proud on the 50 CC, huh? It sure looks better with a round cylinder and head stead of squared off.
I wonder if an aftermarket high quality round jug and head would sell? You know, nice looking fins, etc.
I would even be interested in a "kit". Bored and honed rough casting that comes with a thin file and a few sheets of wet or dry to finish off the fins.

A balanced crank/piston assembly would be nice, too. Just build it up as you could afford it. You listening, Jim?
I might order one of the 50's just in case I ever need a receipt for the state. Are all the 50's round like that? Wouldn't like the local yokels to tell the difference by sight.
Ted