Coverted my 1988 300E to a 5-speed about 8 months ago and have been driving it everyday. I got some great tips from this forum along the way. Got the trans from the pick n pull out of a 190E 2.6. I had a drive shaft made (lengthend the front section) and modified my existing crossmember. The pedals and shifter from the 190E bolted right in. I did have to lengthen two of the shift rods a bit.
Overall it was a fairly easy conversion that took about 10 hrs and got to replace the main seal whie I was at it. The overdrive is great, car is faster, gets better mileage and most importantly its fun to drive now!