John, I had one of these a couple of years back let it go also!
A THIN blued steel bad goes around the reciever & through those two 'Top Hat' mounts. It had a 'L' shaped tab for finger & thumb gripping. To enable the band to rotated slightly.
The band was NOT the same size as the entire circumference of the Reciever. it was approx. 1 Inch shorter. This enabled it to be 'fed' through the two top hat mounting points. & also under the Trig Mech cover. The top hat mounts were BRAZED onto the receiver, not welded.
I heard it was an INDIAN Army Mod, though I cannot confirm this. It seems an overly complicated 'solution' when you see the, 'Simplicity Itself'. British Mod of a replacement bolt handle, & a hole in the Reciever!.....:confused: