Thanks.Good on yer, you made a bike to suit you, not anyone else.
I'm trying to find the correct info regarding the RS rear wheel, I believe it's 14mm out of line when mounted to a 1250. Easiest/cheapest way to overcome that is to machine 14mm off the wheel mating surface but, that's a lot of metal to shave off, I've read that it has been done but, info on this is very patchy/hard to find.
It would make the swap, and swap back, a lot easier and cheaper than changing the arm.
I found the German GS forum really useful re the wheel swap.