Oh if your ordering then get 5.5 will def fit better. Hell really if you can get 10" rim with 6.5 backspace spend the money once. Might be a couple extra bucks but you'll love it in the end alot more.
the 5 inch b.s. should be ok...its going to depend on what tire you use..if you use a drag radial they may be close to outer lip due to the fact of them being a square tire..if you go with a et street a 28x11.5 would be the max but you may need to roll or grind the out lip.. I ran a 8 inch rim with 4.5 b.s. for a long time with 28x11.5 et streets and all i needed was to roll the outer lip in....5.5is the ideal b.s. on 8 and 6-6 1/4 would be the best for a 10 inch rim but most off the shelf rims are a 6.5 so that is why they are the most common on a fox..........remember your rear brake drum or disc is around 1/4 .....Good luck and post some pics