Thanks for the feedback!
'Plug and play' is definitely the goal here. Re-engineer as little as possible. Good news is that the STI diffs are getting cheaper. They've gone down a couple hundred from when I sourced one for my 510 a few years ago. I'd run the same setup for my 280z but I'm working on a potential R200 solution instead.
If I understand your question, the OEM STI inner housing is not swap-compatible with the axle I source. I tried several ideas with no luck.
The R180 STI stubs are welded onto the CV housing in 3 different locations. One weld alon