Tailshaft is basically the right length, but need to change the rear uni/flange over to suit the 720 diff and may as well shorten it a touch while you're at it - at least you have to change the flange in my case as I have the BW diff in my 120Y. May well be that the Nissan/Datsun diffs in the earlier 120Ys might even have the same pattern as the 720 diff, who knows.

Shock mounts are required - very simple change though as they're attached to the leaf mount not the housing itself so there's no risk at all of bending etc. Two little tabs on either leaf mount will be fine... 3mm plate probably heaps but I'll go 4-5mm while I'm going to the trouble of making them.

I'm changing to four-stud, so I'll need to have the stud pattern drilled and the centre machined down to match my wheels. I've decided I'll retain the standard 720 bearing setup, so all I need to do is modify/replace the backing plates, and organise brakes (probably 4st discs from a bluebird if they're easy to adapt).