Grant,
I'm in much the same circumstance as you, as I own a Euro spec M5 which I intend to bring back stateside. It's fairly obvious that the M5 is not your garden-variety conversion, and the horror stories of botched conversions abound. Even if successful, you can expect to pay roughly twice as much as it would cost to convert one of the M5's more docile cousins (i.e. a standard E34 5 series). This makes it doubly important to select someone who has M car experience.
I've really done my homework in this area, and know of only two firms with a history of success with this particular car. My first choice would definitely be to talk with Will Zaraska at Willz Leasing Corp. (
www.willz.ca), but you'll need to be quick, as Will is getting ready to spent a week or two in Germany at the Nuerburgring. Will works through a prominent U.S. RI on the east coast, and specializes in the 3.8 E34 M5.
I've also heard of at least one M5 having cleared the process via Eagle Imex (
www.eagleimex.com), but know little else about them.
Chuck