Alright so I think I'm gonna go with Cobra Transmission. I called them and priced everything out, they have a pretty good price on the extended driveshaft— $310 for a new extended driveshaft. Since I'll have to remove the transfer case, I'll either rebuild mine with a new chain and new bearings or I'll buy a good condition used transfer case and rebuild that. It depends on what the front output splines look like in mine. If my front output splines are okay then I'll just rebuild my transfer case. It's $80 for a new chain and less than $20 for new needle bearings. I found a great DIY on replacing the transfer case chain (
https://xoutpost.com/bmw-sav-forums/...-pictures.html)
I know it seems a little masochistic but I'm actually pretty excited to do all of this. I'll replace both guibos and the transmission/transfer case mount as well.