With 2wd, the rears should be your limiting factor:
5103, 13.6x28, minimum useful setting is a treadwidth of 55.8 inches, so maybe 70 inches overall width.
5105/5205, smallest tire in the manual is the 14.9x28 R1, with the multi-position rear wheels, has the same tread width minimum of 55.8. So 71 inches should be the about the minimum overall width with the small R1s.