Depends on whether or not a 28" tall tire will clear in the front. Personally, I'd go with a donut spare. The 1977-1990 GM B-body cars came with donut spares mounted on wheels with both 5 x 4.75" and 5 x 5" bolt circles, since these cars could have come with either bolt circle. Even a posi diff has to go around curves, so the diameter mismatch won't kill it while you drive slowly to the nearest repair place.
Also consider a tire plug kit and 12V compressor.