If your label is correct, the engine has a 63mm bore and a long stroke. To install a 67mm or 72.5mm bore, you'd need to either enlarge the case mouth or swap cases. A new set of cases is cheap at TB.
That would take you to about 229cc with the 65mm bore and 268cc with the 72.5mm bore. Sounds like fun!
I bet that would push you to 90mph.
