Hi all, time for an update!
So today was productive, a friend and I (mostly my friend) swapped out the ring and pinion from a 4:11 to 3:73 as the gearing was a little high after the manual gearbox conversion. 100km/h (60m/h) was up around 2200 revs, now its down to 1800, right where I wanted it. Given our highways are often 110km/h it was even higher a lot of the time., up around 2400!!
What we noticed: The existing diff, despite only having 250k km on the clock, was rebuilt at some stage given the tooling marks. It was perfectly meshing, LDS set perfect and in all, great condition. The crush tube was changed for for a solid spacer too.
We re-used the solid spacer, even reused the oil as I only changed that a few thou km ago and was still super clean. I didn't take too many photos given I was covered in oil much of the day. I guess the proof of success comes after time but it was all within tolerances.
Next job: I think I have air in the brakes so I want to check them. I'm also leaking a fair bit of oil from the sump, so I'll rip that off and use sealant rather than the gasket - I know, I should have done that in the first place!