A very nice pick up, Paul. Have seen these loops with HJL and RLB rigs, but a very rare to find item either with complete rigs or by themselves. See attached for a complete HJL rig as approved by RZM/MPA (materials acceptance dept.tags still insitu.)
As to value of the loop, I would only be guessing at $500.00 usd as they are rarely offered/traded. Anyway, my congrats on your find of a very rare accoutrement in super condition.

Resize of Rotation of 2009-06-14 064.JPG (74.89 KB, 168 downloads)
Resize of Rotation of 2009-06-14 065.JPG (71.37 KB, 170 downloads)
Resize of Rotation of 2009-06-14 066.JPG (69.25 KB, 168 downloads)