I just got one home yesterday, a 1988 5spd with 229K miles on it. It was someone's daily driver. I plan to part it (less the 5 spd bits) as I'm not interested in the work involved to bring it back up to standard. It runs and drives fine, but needs minor body work, interior work (neglected red leather with a hole), and rear suspension work (links and flex disc), etc. After I check compression I'll list the engine so that someone can evaluate by driving before buying it.
The 95 E320 that mom is using has a 5 spd in its future (assuming I can fool its electronics)
Your 300E shifter will work OK if rebushed and slightly cut down so that the throws are shorter. You will not be doing any speedshifting in any case.