Yes, it would be possible, I have a 50cc that goes 40mph (All of which have 32mm stud spacing) so with the more displacement, it would definitely be possible. To get 40 MPH out of your bike, I haven't done anything crazy; HP carb, Jets, sanded cyl head, NGK spark plug, CDH66 exhaust, OZ carbon fiber reeds, 36T sprocket. So if you did a similar setup on a 66cc with 32mm spacing it is possible to get 45MPH out of it, and with mild porting and a bigger carb, you could get 50MPH out of it. The one problem with 32MM spacing is getting a nice reed valve on the engine. My dad and I made an adapter to put the 40mm reed on a 32mm engine and it works great.
To summarise, yes its possible to do with standard mods.
-Dan