You could have yours regeared, or get a new multi drill companion flange. You could use any differential housing you happened to have.
Also realize that before 78, all were coarse splined on the pinion and thus weaker. 78 only they were 4.11 and fine spline pinion. After 78 they were 3.70.
But seriously any housing from early to 97 would work, so I don't understand the specifics. If it's the flange, all combinations of coarse and fine, large and small are available.
I have a 78 fine spline 4.11 diff in my spares pile, but between the shipping and the unknowns of whether it's really ok or not, why not just get a diff rebuilt to your specs?
Ok, after a few members reaching out to me and a long thought process, I'm going to make the switch to the 3.70 gears. This will be more conducive to the way I drive my FJ40.