How about Albrecht Stachel, "Chief Bottle Washer" at Brooklyn Motoren Werke in Brooklyn, Wisconsin? [Just south of Madison.]
I don't personally know him or his work, but as a former midwestern lad myself, and one who used to style my (quite modest) operation there (in Iowa) as "Clarke Streete Carriage Werkes" -- blush: it was a long time ago and I was actually trying for irony -- I've long been intrigued by this apparently broad-spectrum and high quality Mercedes specialty house located in a large barn near a tiny town named Brooklyn.
You can get an introductory feel for the Bottle Washer and his Werkes on page 70 of last fall's Star magazine out of MBCA, where the first of his "regular technical column(s)" appeared in the September/October issue.
Best luck with the quest. Please keep us posted as to what you find and how your friend's project goes.
Denny