TBH its all down to the offset, I have a set of 7" teledials on the back, thats a combination of Late rear hubs, but with a mercedies disk over the top, this probably increases the track by about 10mm each side, on top of ths I have a 10mm adaptor, the teledials I have have an offset of 52.3 so they tuck in nicely.
you could possibly get away with an 8" wide wheel as long as the offset is high and you have redrilled hubs.
Mark