Well, I did a swap from automatic to 5 speed on a E30, and it isn't too bad of a job, you need to pull everything from the flywheel to the driveshaft on the 5 speed and remove all the automatic stuff and install the 5 speed stuff.
It takes a lot of time and you better have a nice collection of tools and some friend to give you a hand to pull the trannies out. If you are a good shadetree mechanic, all should be good.
'85 Euro 635csi Race Turbo, megasquirt, Group A
'92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
'02 Subaru WRX Wagon with STI springs, bigger sway bars