Mercedes had a column shifted four speed which would have had 5 positions and presumably 3 shift rails (I don't know the details)
that might be something to look at frist, might get you the column mounted stuff capable of 6 positions as a start.
One complication I see is the T5 is a top shifted transmission, not a side loader with different levers like most column shifted transmissions are/were. That makes it tricky to mix and match linkage when they're two completely different designs.
I vote for the floor shiftier, always seemed like a much better and simpler design to me.
Grigg
