Interesting ideas guys.
When I first looked at it and the mounting flange at the top, I was thinking that some type of compression driver might have been there. After thinking about it for a while, I figured that this might not be so. The photo from the rear of it is pretty dark(sorry) but it looks like the horn was mounted to a vertical sidewall of some kind. This would not allow for a driver to be mounted at that connection I wouldn't think. I believe that the flange allowed for connection to another length of "horn" or something. That is if it even is part of a horn of some kind.
The raised number 8179 in the casting should shed some light on the manufacture I would think.
Maybe some day, I will find the rest of the Lighthouse if thats where it came from
RC