Head studs, go with ARP:
You can replace one bolt at a time so you don't even have to remove the head. The m21 turbo diesel manifold won't fit the M50 head, and the turbo that it came with is way too small for your use anyway.
This might fit your head, but who knows if it will fit in your car:
You could always just get it, and get it modified to fit. The flange will bolt up to the exhaust side I'm sure (but you should verify) so at most you'd need to get the pipes moved around to make it fit in the E34. (Though I think you have more room than the E36.)
What are you going to use for fuel? Get Barrie to tune a chip for you?