Dave at Ottowerks (who built my E9) is very knowledgable about the E39 as well. He worked on my E39 M5 for several years and was phenomenal. Further, he's done PPIs for several cars that I and other customers that I have referred to him have bought - and not one person has had a complaint.
Dave Grisel
Ottowerks
415-512-1975
You would have to bring the car to him in SOMA (right near the 101), but the deal in the past has always been to have folks show up with cash and/or a check, and if the car passes do the deal right there.