It is not a hard conversion to do, especially if you have a donor car to steal from. There just happens to be one for sale in the Swap section, a 1986 300E 5 spd. Probably 90% of the parts are the same and with the A/T diff gear ratio you have, it should run well. The 300E is in Carlsbad, CA but don't know where you are. Sometimes a salvage yard such as Potomac German has one. The pedal cluster, tranny and most parts except the driveshaft (length) are the same.

Don't give up...

Tobias MB
C280Sport, 300CE, 400E, 190/5.6