Getrag 260 doesn't have a removeable bellhousing and a port for mechanical speedo drive. You can use a getrag 260 but you'll have to use a GPS device to keep track of your speed since BMW used an electronic speedo for models that used this gearbox. Keep looking for a getrag 265 since it has a port to insert your mechanical speedo cable. They are out there but getting much harder to find these days. Getrag 265 came on 80-81 E12 528. 82 E28 528e (but you'll need a M30 bellhousing with this year only eta model). Correct me if I'm wrong, but I believe 80-81 E23 and E24 also came with a getrag 265. For 85 model year only, BMW went back to the getrag 265 due to getrag 260 issues on the E23, E24 & E28 (535i). For the 85 model getrag 265, the speedo port is there but no speedo gears in the gearbox. You'll have to use the speedo gears from another gearbox. Here's a perfect example of a getrag 265 donor car you are looking for.
http://sfbay.craigslist.org/sby/cto/4599966092.html You can use parts from the donor car to convert from carbs to L-jet.
G-Man