What crownwheel do you need ? I think the earlier Skylines use a high 3.x range and their drivetrains are robust.

The later R34 stuff is in the 3.5x range...much better IMO. The R34 front diff is integral to the sump.
I think I posted pics of that before where the guy was fitting one to an old Celica ?

Other option is a normal IRS rear diff, inverted. Same F/R