Do you happen to know what t-case is behind that ZF5 in the e99? I've never looked close at an earlier SD with a 5 speed to see what T-case they used. I would assume it was a NP271/273, but it would either need a smaller splined input shaft or the ZF5 would have to have a larger splined output shaft as compared to the earlier versions used in OBS pickups.

 

Here's some good ZF info from the source.
Scroll all the way to the bottom.


ZF Friedrichshafen AG USA/Canada | Print Catalogs

 

From what I can tell SD 4R100 and ZF5 transmissions were kept 31 spline outputs while the ZF6 was a 34 spline. So, the auto t-case should bolt onto the ZF5.