Frame identification

I am planning on getting a Mor Ryde pinbox for my fiver but I need to figure out who made my frame. As you can see it is an Avion by Fleetwood made in 1991. There is a small plate welded to the front of the pinbox but time has taken it's toll and it is unreadable. The trailer has torque tube axles like an Airstream. The current pinbox is just plain steel, very short, canted forward. The pin is 3-1/2" back from the front edge. It measures 11-1/4 front to back and 11-3/4 wide. It has 4 sets of holes but the trailer flanges it is bolted to only have 2 holes which hold large bolts that go all the way across the pinbox.

Does anyone have any idea who's frame this is?

Bob