I would think SBP and BBP 7&1/4's are the same fairly close width (but I would do the swap & especially on the front discs then measure). Likely with some care you could get a good measurement without the tool. As you know the rear panels on the insides ain't plumb and on the front I think you'll run into an OD problem before a lock to lock interference problem. I would be rounding up a set of 14x5.5 BBP rollers to slap on there so you can measure (rim clearance/offset/sidewall bulge) and the SB will be listed for your choice of tire. the tolerances on the early A's were the worst (I love em tho) & are even so bad that a tire that fits on the dr side front may not fit on the pass side front! A guy on here had that same problem.