That housing is a stock GM housing. There was a temp sending unit installed there that controlled a vacuum switch.
Below are two photos from different angles of one that I have. There is a casting number on the housing. It is 336773 then about 1/4" gap and then the number 17.
Left click for a larger view.
Last edited by Frisco; 08-18-2009 at 09:51 AM.
Reason: added photos and casting number