Don't know how helpfully this is but. My brother got his gng mounted on his Specialized Big Hit which has a 73mm bb. He got in touch with ES member Lightening Rods who builds custom brackets for gng kits. Maybe worth PMing him for a bit of advice?
Yes I think his sheets will work with wider bbs, and spacers. Otherwise he's got specific sheets for that size.
Either way, send him a pm cause you're going to want his sheets down the road anyway