The 80cc (75 really) drop right into the X50 engine.
If you just have the kick assembly you are shit out of luck unless you have a friend who is a machinist and you can get your hands on a kick start clutch assembly.
There are 2 holes in the case that match up to the tranny cover/kick start assembly. These locate everything preciesely and take the strain off the bolts.
The clutch on the kick start is special as well. There is no friction material on the outside face (where the preassure plate would connect. Instead the surface is just a metal plate. There is a gear that slots into this plate and is held captive by a bolt on the end of the crank shaft. This gear meshes with the gear on the kick start assembly. Both are precisely machined and hardened to minimize wear.
Not saying it can't be done but just that I would take a lot of work to adapt the side cover to a stock e50 case. Without the benefit of the case accepting the 75cc kits that the X50 case dose.
I'll upload some pictures of my case tonight or tomorrow