Whadda score!!!
Nearly all that sun roof stuff came from this source back in the day, same folks that did many of the "t-top" conversions for deetroit inna offline mode:
asc | American specialty cars
They had/have installation operations around the country.
And this is the kinda stuff they do:
American sunroof corporation home page
Looking at the leading edge of your roof insert, it doesn't look like it has what would have been a custom-molded filler piece where the frame meets the sheet metal to fill in/seal where the stiffener ribs are in the roof panel. But I can't really see that, check it out and see if it's filled with dumdum, permatex #2, and rtv/bath tub caulk!
If it was a true "asc"-type install, it would have a gasket/seal that was molded to fill that space real neatly. And somewhere on the frame, you should find the logo stamped in (May be hidden underneath) for the manufacturer. An asc would also have a water drain system that went under the headliner and down the inside of top somehow like a gutter. Don't remember the other aftermarket units having that feature since they weren't considered "oem" quality.
Back in the day, you could find "universal" sun roofs at any auto supply, just like slider rear windows for pickups!