Sorry about the late reply to this thread, but I'm new to this forum. Since your bike has an 80cc engine, it has to be registered as a motorcycle for it to be considered legal. Anythig over 50cc is a motorcycle in PennDot's view. The predicament we both face is the lack of a title for such a bike. There is no VIN number to use in titling as well. One route I've considered is to use the serial number of the engine (provided there is one) and getting it titled through an out-of-state titling agency. This route is the way many people go when building a vintage car or street rod up from hulks that have no title. If registering it as a motorcycle, you'd then have to get a motorcycle license and probably add turn signals to the bike (but I'm not 100% sure about that).
In my case, I have 48cc engines on both of mine, and with that configuration they literally fall in between any description PennDot has. It is not a Moped because it does not have an automatic transmission, yet it complies in every other aspect. I have gathered much paperwork from PennDot regarding trying to register my bikes. One part of the PennDot paperwork I have states that mopeds need not have a title, but here's the rub. Later on in the same paperwork, it states that no vehicle can be registered without a title. It seems as though one hand does not know what the other is doing at PennDot.
I gave up trying to register mine. The local police don't bother me, in fact they are familiar with seeing me putter around town. One day, one policeman stopped when he saw my Columbia, which is very retro looking. He stopped and asked me if it was an antique Harley!
He told me that the local cops won't bother me, but if I see a State Trooper to kill the engine and pedal. So far the State Troopers haven't bothered me either, they've just waved as they passed me. In my area, as long as you're not a kid or doing something stupid, they don't bother you. With some of the conveyances the Amish put on the road, they're used to seeing just about everything.