[Boatanchors] General Radio 1931-A Modulation Monitor

[Brian Harris via Boatanchors]

I recently acquired my second General Radio 1931-A Modulation Monitor.  This one is a much later serial number (2688) than my first one (370).  On the front panel of this second is stenciled the following:

AF33-604-16827
7CAC-575975

First question:  Can anyone shed light on the nature of this stencil?  Might the AF mean Air Force?

Second question:  These units required a coil specific to a frequency range.  I have two coils, both of which cover .5-8 MHz in four ranges.  These are the most common coils as these units were most often used with AM Broadcast transmitters.  I would like to obtain one or two of the higher frequency coil, which I recall covers 8 - 30 MHz.  If there is an outside chance that you might have one or two of these available please let me know.  Of course I can fashion some myself but that is something I'd like to avoid.

Thank  you,
 
Brian Harris, WA5UEK 
cell 214-763-5977 
email cosmophone at yahoo.com