The R engines are silver, the GS is black! That alone..........
I'm sure we could theorize all day. You have to put them side by each. I've worked on enough of either and i don't see it happening. Being different colours means that the pn's will be different even if the part is otherwise identical so you'd have to investigate. Don't forget one is belt drive and the other chain and I know the output shaft is different so no swapping sprockets.
I'd say it was a waste of time but then I'm not that bored yet. There are turbines and diesels in bikes though. Like I said, if there's a will.....