No problem, this has been done many times. this is a DIY project, just have to have all the parts. It is pretty much plug and play.
I just did this swap in April this year and already have just over 10,000 miles on it.
As I understand it, you have a 85 300D, correct? and you want to install the 240D manual trans, just so Iam on the same page with you.
here are a few threads on the swaps done, and some good reading to get up to speed.
www.peachparts.com/shopforum/showthread.php?t=146636
www.peachparts.com/shopforum/showthread.php?t=159597
www.peachparts.com/shopforum/showthread.php?t=223847
www.peachparts.com/shopforum/showthread.php?t=87256
www.peachparts.com/shopforum/showthread.php?t=88699
www.peachparts.com/shopforum/showthread.php?t=206755
the 85 for some reason and maybe some 84`s, MB made the hole in the crank a different size so the standard pilot bearing will not work. you might have to have a bushing machined to fit in there.
This thread by TOMJ is a good one, detailing what he went through to get it to work. best way to do it though, is make a bushing.
www.peachparts.com/shopforum/showthread.php?t=76297
Charlie
Later on TOMJ mentioned where making the cup in the above thread idin`t work, the bearing spun.
www.peachparts.com/shopforum/showthread.php?t=213438