Just a quick update to the thread, I think I'm leaning towards the M54B30.
The more I read about it the more excited I get about the prospect, the key things I like are:
1) There is an example from BMW of that engine in a e36 chassis (2000-2002 Z3 3.0)
2) It uses the MS43 which seems to have been opened up by the community, this is a big plus.
Im thinking the most economical way to go about this would be to find a Z3 3.0 donor car, so I'm starting to hunt around for that now.
In the interim I've been driving the car around a lot and am loving it even with the M44
.
Probably gonna be busy for a while just fixing lots of little things, and upgrading non-drivetrain relating components.