Hey mate, Great little project you have. I was going to go with the rotor conversion but opted for the SR20. I have stuffed around with a hilux and by past experience oit is worth trading your 6 stud compete diff for a 5 stud from the start. You basically have top change everything from backing plates. axles etc. They are basically 2 different diffs. After alot of research on the hilux diffs i have now got a 2wd from a 86 model. I know that a 1976 2wd hilux diff will fit into a mazda 1300 without beign shortened. But good luck trying to find one which was the problem that i had.
Good luck with the rest of the project