Hot Rods Identify - Vent Window

I have this extra vent window came in a car I bought but have no clue what’s it for. If it helps the guy I bought the car from was a Chevy guy, also has a 41 Buick Conv. Thanks in advance.

 

Square top probably means convertible or hard top.

 

It's clearly a hardtop or convertible piece, no way that was from a sedan. It's also got a spot for a crank out regulator, that's a clue. I found pics of a 51-52 Buick hardtop/convertible vent window and that was close but not it. Not sure on this one.

 

This is close but the numbers are off a bit. Obviously , it’s from the opposite side.