re: 60 MPH...achieveable? Who cares?!? Let blueprint an engine!
I don't doubt it can be done, a 49cc engine can be tweaked for at least double the power the stock engine turns out. I had a 1964 Yamaha 80cc two stroke motorcycle with four speeds that would easily reach 55mph, so a 49cc pushing a lighter bike should do it.
Goldwing 1500, Silverwing 600, Schwinn 49