Moped Army

I have a 1979 Batavus intercycle with an M56 engine on it currently. It is missing quite a few small obscure parts, and it seems like every belt I have ordered for the thing has been too small. What I really want to do is replace the motor with a 70cc or higher motor and exhaust. How difficult (if even possible) would this be to do? ...and where is a good place to find such a motor in its complete form with all the parts ready to ship? I live in suburban Kansas, and there is a non-existence of moped or even moped knowledge here. So any help would be greatly appreciated!!