Matt, I just stepped out and measured mine at 53.5" from the outside edge of the knuckle to the outside edge of the knuckle. I think this is where the backing plate goes, but could be wrong. Basically if you look at the pictures in my disc brake conversion thread - I measured from end to end of what is sitting on the jack stands, not including the birfields hanging out of the knuckle.
Ricardo Maestas - Bio Page
1999 LX 470, 1971 FJ-40