[R-390] Can you please help identify this?

[RLucch2098 at aol.com]

Hi All;
I know this list in for R-390's but milcom List seems to be dead, maybe 
someone can tell me where to ask if no one here knows?
Now, the unit:
It would be nice to know its use & possible Part Number.
I know the name marked is Beam-Finder.
Seems to be an Audio filter & works nice.
Any ideas?
Pics:
http://www.myradioroom.com/navybeam-finder1.jpg
http://www.myradioroom.com/navybeam-finder3.jpg
Tnx & 73..
Rich WA2RQY