Thinking about turbo on my/6 again...

You don't need to go crank fired for the EFI route - although conversely, you could go with a crank fired ignition and carburetor if that's what you really wanted for some reason. If you want a crank trigger on a slant six, here's how I set one up. But the easy way to go with electronic control would be to use aftermarket timing control with a Lean Burn distributor. I'm doing that at the moment and plan to switch to the crank trigger after sorting some other issues, like why my fuel gauge reads way too low.

There isn't that much I would recommend stripping from a BMW for an EFI conversion. Some of the early to mid '80s motors have a plenum that has bolt-on runners, which you could potentially use with fabricated runners. But the manifolds are designed for cross flow heads with equal port spacing, and from the early '90s are made of plastic, so lifting a whole manifold is not a good idea. It might be possible to adapt their external crank triggers. But I wouldn't try adapting their electronics; their stock ECUs are not something you could tune enough to adapt it for an engine with wildly different fuel and timing requirements.