I have run with 10mm spacers for years with no problems and have seen spacers on other quick cal lookers. I think the area I would pay attention to , would be the wheel studs, as they have the extra leverage acting on them, high quality m14 press in studs might be worthwhile.
I have m14 press in studs already in so thats no prob. Interesting about the Fusch's Neil and Lee (yep, got the right car Neil, I'm on GB's) I have been toying with the idea of changing to those. The offset quite different is it?