Originally posted by Glen
The 190E 2.6 5-speed should bolt in with minimal fuss and I believe the 190E 2.3-16 Getrag tranny will bolt in too.
Note that there are 300E 5-speed manual cars out there too. They were imported in 1986 and 1988 and the swap would be relatively straightforward. They're rare...about ~750 '86 cars and maybe half again as many '88 cars. You have another option too, the '91/'92 300SL was available with a 5-speed manual as well.
Forget the 2.3-16. They go for a pretty penny, when they come up on the market. Same with the '86 and '88. Too few of them. People who have them, keep them. And when they come up, everybody jumps all over them.
Does the '91/'92 300SL have the M103 engine? That might be another donor car to keep a lookout for. It looks like the 2.6 5-speed is the best bet.