My main driver is an '88 300E with a five speed. There are only about 300 '88's and about 700 '86's that were shipped to the US as US eqipped cars. I too love driving one of these great cars with a stick.
As far as conversion, there is only one way I would attempt the transplant and that is if I had the ENTIRE donor car in the shop next to the recipient. This is the only way you could get everything exactly right.
My 300E is starting to get a little run down at 242,000 miles. It will go many more miles, but my thinking is to find a really nice, clean, low mileage 300E and use my current car as the manual transmission donor car. Then the rest of the car would be a parts car from there on out.
I love these cars enough that I would go through this hassle, but again only with the entire donor car at hand.
If the Euro wagon you looked at could be had cheap enough, you might consider the same approach.