What's the deal? Hinge Plates Installed On These JBL L-100's

[basicblues]

I recently aquired another set of JBL L-100 (late) speakers. These came with a hinged plate mounted on the bottom, the hinged is located at the front of the speakers so the speakers will tilt forward. The plates are professionally made and fit perfectly and I was just wondering if these were an original JBL product and what was the intended use or purpose? I feel sure I've seen these hinged plates before but cannot find any information about them. Check out these pictures and let me know what you think. Thanks

[Wagner]

Picked up a pair back in May.
Original owner had installed LARGE ball type wheels on them.
Protected the bottoms though, and the corners.
Only gripe is that he made certain to install all 4 screws for each wheel.
They were large enough to support a piano; (2) screws would have been more than enough.
32 little holes to fill, but that's "ok", got 'em for a song.

Don't know if that's JBL or not (I doubt it, would have seen it more often) but it would certainly allow for adjusting vertical axis firing angle.
Seems like something's missing?
Lots of '70s era aftermarket stands were big on the backward tilt.

Thomas