60mph, thats about 96km/h. This was achieved in the fifties with moped technology from the day, ie no exhaust chambers.
the 50cc record stands at about 145mph or 233.3km/h
some ideas of what it takes and an interesting timeline
10 speed gearboxes, iced cylinder heads, disc valve induction with various forced induction setps using exotic fuels.
50cc road racing was popular back then.
I like the Kreidlers, broke many records