Hi there,
what is not clear to me is why you want to change the final drive of your r12s if you just need bags ... There are bags available for the r12s:
However if you think these are not suitable and you want other bags it is not a matter of the final drive but of the rear frame. But if you implement the rear frame of another model some serious mods are required (including moving the exhaust ...
Brgds
Oliver