W124's only came as a 5 speed for the 300E in 1986 and 1988 in the US. In Europe they were very plentiful throughout the 85-96 range of the 300/320E , even with the M104 motors.
I have the 717.432 5 speed box with a 190E pedalbox, which is bolt in. Aside from the box, clutch, and pedals, a manual front drive shaft and x-member has you out of the misery of the slushbox.
I don't have anything too cool for it, but I am modifying the ASD system, which is a hydraulically locking rear diff originally run through the ABS System in ECE cars. With any luck I'll have a cabin adjustable lockup on the fly with the clutch LSD out back.
But for right now it has the most terrifying thing I've ever seen in my life, Bosch Electronic Constant Injection System (CIS-E). Priority 1 is throwing it away for EFI. I may add a camshaft and 600cc's of displacement while I'm at it....
Look at it, it's horrifying!