I was getting sick of the diff noises so i swapped the mfactory helical back into my original diff. Decided to do it myself to avoid the shipping hassle and buy the shim kit with new output shaft bearings from difflabs.au. Since i had 4x original shims from both diffs including thinner shim i could build up, figured i could make most sizes without needing to get them machined down.
After a bit of fiddling around with different sized shims i got the backlash and gear pattern looking like it was originally. Backlash @ 0.09mm down from 0.14mm so clunking\knocking mostly gone or much quieter. Unfortunately still have a similar gear whine when cruising ~110kph. Both diffs have wear to some extent, but i can only guess based on the previous diff being ok before the solid subframe mounts and\or meyle front diff bushings that they are allowing more noise to be transmitted.
The plan now is to convert most of the suspension back to 'OE' spec, chuck in a replacement open diff and sell it when economic outlook is better. I did plan on keeping this but i find i don't really desire to drive the car after converting my Ti to manual. Given the state of the average road these days its very harsh (compared to that) and only really enjoyable when driving fast\hard on decent condition ones. The 80's BMW ethos is what drew me to them nearly 2 decades ago and why i had E30 for 8 years.