A motorbike has a VIN number, im not sure if you could get a motorized bike registered, im not 100% sure, but even if you could you would then need chain guards, blinkers, brake and tail light, full wheel guards front and rear, DOT approved tyres not to mention you would have to pay rego, would require a license, DOT helmet. Would have to follow ALL road rules and not be permitted on footpaths. And all that for a bike thats lucky to do the speed limit. Youd be better off buying a moped...... not what you wanna hear but thats what its like in QLD, ive been thinking about this topic for a long time now....
Or if you have the skills you could buy an old moped, register it, then cut it up using the VIN number and make a bike with the moped motor or find something better..... ive considered this and making a full fendered boardtrack bike but i figure electric will be easier and i will be allowed on the road and also the footpath, providing you ride with care. A big plus for me with the electric is i plan to use it to commute to work, when i encounter traffic i will legally be allowed to pass the stationary traffic on either the shoulder or footpath, whereas if i had a moped or motorcycle it would be illegal for me to pass.