After stripping out 16 swingarm of 16 frame tonight and fitting RK5 swingarm in it's place a couple of things i discovered,it's far easier in my opinion if your doing RK5 swingarm conversion on either an mc16 or R2J to weld similar rear brake caliper lug on swingarm!To start grinding away at the webbing inside frame is not a good idea
A problem you have if like me your modding a 16 the rear wheel spindle is 17mm compared to 20mm rk5,i'm guessing r2j is 20mm also,so i can either get r2j bracket or machine 16 bracket out to 20mm i reckon theres enough meat there to do this without bracket breaking and then at least i'll be able to use my 16 rear caliper as disc size is the same
cheers Rob.