I can't shed too much light on skyline specifics... but I did go to some effort with my Y34 (same rear end as Z33/V35 for the most part). Sourced an R34 GTT helical diff, and even just looking at the centre while they were still in the housings, you could tell it wasn't going to work. I got told it would work if you swap over the half shafts etc, but it needed some serious shims at a minimum.
I ended up getting an NM35 helical diff centre and took it to the diff workshop. Even though it was "bolt-in" one of the half-shafts needed to be machined down to work. $150 for the diff centre, $550 labour. So it worked out well for me, but I was lucky to sell the R34 diff at the same price I bought it... not to mention the time it took me to gather all the bits, disassemble, compare etc.
Lesson learnt: it is easier to just buy an aftermarket swappable centre, even if its pricey UNLESS you are 100% sure of a direct swap (and by 100%, I really mean 100%).
Upgrading diffs was one of the best mods I did. Car drives so much better. Next to no wheelspin, ever.