Metric Mechanic Inc – BMW Performance Engines, Transmissions, Differentials & Custom Parts - Metric Mechanic
I visited their shop back in the early 90's. I have heard great things about them. While I don't have personal experience as a customer, I suggest you at least check them out and see if they can fulfill your needs.
Back when I was into 80's BMW's I read hit or miss things about this place. I think in the 80's and 90's they were real popular and well known but over time I guess they overgrew. I've also seen people talk about how the quoted HP/TQ figures and flow rates for the engines & heads they advertise are stretching the truth to put it lightly.
Metric Mechanic 3700 - MyE28.com
metric mechanic is really for the vintage stuff though, they wouldn't be on my mind for something like an E46.