Navi uses a CVT scooter drive transmission that ends at the rear wheel, G7S has a unit construction engine and transmission that ends at the countershaft sprocket, so no, the Navi is not a desirable engine donor.
Electric conversion is easy without messing up anything on the frame, put a full fairing over the whole thing and it would be a little stealth rocket. If you find the correct ICE engine for it later you can go back to original. It's nice to have that option. All it takes is bags of money, and somewhere to plug it in when you are not riding it.