To help shed a bit more light, Mercedes used vacuum on these cars for much more than most manufacturers did. Vacuum door locks, vacuum pods for the climate control, etc.
The vacuum shutoff is integral with the ignition switch. Those who have done swaps like these have had to figure out a way to draw vacuum on the fuel shutoff valve when turning the engine off. You could make it as simple as having a tube in the car that you suck on to turn it off -- your passengers will just need a brief disclaimer
The transmission, as noted, is a more complex setup but it's "stand alone" in that it will move over with the engine and transmission and should continue to function as it did in the donor car. The only line that enters the car, if any, is a vacuum bleed off for the vacuum control valve on top of the injection pump. It's not connected to anything, just open to "clean air" in the cabin.
Best of luck!