Broken rear window in cap
 

Hi, I bought an f350 with a matching cap last year, the po had broken the rear window, and covered the frame with a piece of plywood.I'd like to take the window frame off the cap and take it somewhere and get new glass or plastic installed in it. Don't know what make the cap is cause there's no tags inside or out, was thinking about a auto glass place, or hardware. anyway. has anyone taken the frame out of their cap? It looks like it just slides on a rod, but mine won't slide, acts like there's a stop on it but doesn't look like it.
Any ideas. Thanks

Pics man pics so we can have an idea