Jeez, Yorkie. I thought something was cookin' with you asking abut the SPS motor........good luck to ya mate
I think the S4 frame is a different beast to your M600 one. Not sure how this will affect the under tank issues to be honest.
The S4 tank may not even fit???
Can't profess to knowing much about this conversion but I thought the rear of the 4 valve casings, where the swingarm pivot goes thru', was wider than the the M600??? Will your swingarm fit?
Anyhow, if you're ever struggling or need the odd part or two, give us a shout. If I can help, I'd be happy to
