I posted this somewhere else, but photobucketed it so I could put it in this thread also-
heres a domestic NV3500 S-10 tranny, with a 123 chassis 5-speed in the middle, and a 115 chassis 4-speed on the bottom.
The shift linkage for the two MB trannys would put the shifter about 8-10 inches beyond the NV tranny, right about where the NV tailcone ends I think. If you were to get the NV into your MB, the stick would come up somewhere under the climate control in other words.
I have an older late 80s chevy transmission out of a van which is closer to the MB size, and also has a positionable shifter, ill get a pic on that later on, but if it could go straight back it could possibly work. Some kind of Tremec variant. Its actually a 5-speed out of an Astro minivan, so just about as rare as a 123 5-speed. But the transmission might be common to late 80s chevy products, I have to run some numbers