Like I mentioned when you called in, if the diff is from the back end of a 4x4 then it should be an 8" (wouldn't be an 8.4" as the e-locker was only offered in teh 8" at that time). You hadn't mentioned how you realized it to be a 7.5" diff. I would try to verify the ring gear size as the code could be different in the newer vehicles. The only 7.5 truck diffs are the back end of 4 cyl. 2wds and the front end of IFS Hilux's and Tacomas.
Brendan