I've been and checked my diff, and it's definitely 7.5" with 100mm lobro shafts.
I'm also certain it's open (or if it was LSD it's not any more!
). There's no tag plate, and i bought it off ebay, but on the back it's got 3.92 written on in yellow paint pen, and the ratio of turns of the input shaft are approximately that so i've got no reason to doubt it.