That view makes me even more sure it's a window riser mechanism out of a old truck or car. Those countersunk phillips screws look mighty familiar for the inside of a door, under the interior upholstery. Right to the left of the rightmost screw is the shaft ( the end is broken off ) that the window riser handle attaches to.
Back when the side windows weren't so big and curved a lot of the smaller vehicles just had a cable mechanism to wind the windows up and down.
I've seen them in old Nissans, Toyotas, Opels, VWs, etc. 50's 60's.
The P-39 had roll up door windows, I wonder what it's mechanism looked like ?