[R-390] 390A test jigs

[W4QG]

All,

I acquired a set of 4 devices which appear to be test fixtures/jigs. 
They appear to be commercially made.
They have markings similar to what would be found 390(A) modules.
Stamped on them is "R390A" "CODE 26916" and the part numbers 150-017274, 
150-017275, 150-017276, 150-017277
I've looked through my meager documentation and can't find any reference 
to these.
Can someone give me some info on them?  (pictures available if anyone is 
interested)

Thanks,
Paul W4QG