G'day Thomas! Ron" Mercmad" here. I was searching on line for a retro styled air con for a 220SE cabrio a customer has .The car is in very nice original condition so the owner need something that can be hidden .
I like your idea of using the W108 (?) fan and ducts .
but this is what I found a a couple of years ago but cannot find the link again .I am sure the guy making these is in Germany. Have you ever seen them ?
Cheers! Ron B.
Maybe you are lokking for https://www.autoschmiede.com/marktplatz
Greetings from another Thomas