Hi there,
I don't know where you can get the aluminum housing, but I just installed an Unwired Tools digital servo upgrade kit in my '79 450SL, and it works fine. I did call them to ask a question, and they said they have a new upgraded kit that puts all the parts - the control unit and the vacuum solenoids - in a metal box, which should make the underhood appearance a little cleaner than mine is. They said they will upgrade mine free if I choose to do so.
The digital upgrade eliminates that black control unit that has all the vacuum hoses, wires, and heater hoses attached to it. It replaces it with a small digital control unit that operates a simple heater valve in pulse width mode, similar to what the newer climate control units do with the monovalve.
Regards, RGW
'82 300D/4.3L V6/T700R4 (over 70K miles now, no probs)
'79 450SL
'75 280C