[Milsurplus] Possibly rare TBX-8 accessory ??

[J Forster]

Recently, I turned up a neat little box in the estate of a SK that is
unfamiliar to me. The stencils on it say:

     CGQ-60133
     Crystal Calibrator and Monitor
     For use with TBX-8 Radio Equipment
     Garod Radio Company
     Contract  NX SR 71254

It's a little (2" x 4" x 6") OD box with a 10 position rotary switch [A
through J], ON/OFF switch, ANT binding post, and a sealed Phone jack.
Inside is a single 3A4 tube in shield, locations for 10  FT-243
Crystals, a "D" cell holder and a place for a B battery.

The crystals in the unit:

Ch 340   7425 KC
Ch 346   7575 KC
Ch 349   7650 KC
??           16880  KC   xtal for TDQ

Is this a common unit? I've never seen it referenced anywhere. Is there
any doc on line for it?  What B battery does it take?

Thanks,
-John