The transmission and for that matter, the rest of the drive train. turned out to be extremely simple, as no modifications were needed to the transmission mount, driveshaft or rear end.

There are a number of things that need to be hooked up on the transmission.

Cooler Lines - because we're using the stock radiator, the cooler lines hook up with no modification. The lines were probably removed to replace the engine upper oil pan, so make sure you've got new crush washers to install to prevent leaks.

Bowden Tube - actually if you left the engine and transmission intact the Bowden tube should not have been disturbed

Vacuum Connection - depending on the year of the donor, you may or may not have a vacuum connection. This just connects from the "blue saucer" device that will be covered in the Vacuum section

Kickdown Solenoid - the kickdown solenoid from the 380SL just plugs into the rear of the 300D transmission

Shift Linkage - the shift linkage just attaches in the stock manner - nor shortening or lengthening is required. (You may have to make a minor adjustment for the reverse lights, and the park start switch to work properly.

Speedometer - you have a choice here. The 300D is a mechanical speedometer, so you can swap the innards of the speedometer and use the cable or you can keep the SLs electronic speedometer and rig up a VR sensor to the driveshaft and go that route... but that's another topic altogether which is covered under Gauges.

There are two things to be aware of.

Neutral Safety Switch (NSS)

It is very possible that there will be a mismatch in the connector configuration of the neutral safety switch. In my case there was. I needed to change the connector from the 380SL style (722.3x transmission) to the 300D (722.4x transmission).

The simple solution is to just cut the connector off and splice in the new connector, however I chose to leave the 380's connector intact, should I ever want to go back, and fabricated an adapter pigtail.

Here's the pigtail I made to adapt the two connector types.

Just cut a junk yard NSS in half

Then solder the appropriate wires to the two connectors and fill with urethane, epoxy or silicone to prevent oxidation.

Yoke

To properly connect the OM617 and transmission to the driveshaft, you will need to use the 380SL yoke and flex disk. This is extremely simple to pull off nuts holding the yoke on both transmissions and just swap them out. Make sure you torque the nut and stake it properly. These nuts are theoretically single use so act accordingly. In my case the point where the nut was staked was 180 out from the previous spot, so I elected to reuse mine.   

The nut takes a special deep socket - 30mm or 1-3/16