You can in theory yes. In practice it's a lot of messing about and to tell you the truth i just use the kickstart on my re that i fitted.
For the leccy to fit on the r you would need.
The flywheel reversed on the crankshaft. The statorplate. Drilling through the crankcases to mount the motor. The generator cover drilled and tapped to hold on the dtre coils. Then you would need to splice the wiring loom to get the leccy in. The side stand switch needs to kill the leccy as well as neutrual switch.
The list probably goes on but i thought i would just scratch the surface. The easiest thing to do is to use the kickstart. If you're still not happy then transplating the engine and loom is thenonly other viable option.