I never did it myself, but do a google search. There are a lot of hits on how to measure wheel backspacing. I think the best offset for regals and gn's is 3-3/8" or 4"
Are you willing to split them up? Probably not, but if you are, I'll take 2 if they're 3-3/8" offset. I'll have to check my wallet first, then I might take all 4.