Boeing B17 Part ?

I have had this for a few years and cleaned it up a little this morning.

I was originally told it was B-24 – but the Boeing inspectors stamp suggests otherwise.

It is 2 ft long and has two stamps to the rear – a B with an A in the top section. An H with a number 102 (?) in the lower half.

There is a part number – a letter ? followed by 15 7600 14 with the 14 crossed out and a 13 added after.

Can anyone confirm its id ?

Also given the shape is it a door or window frame ? It had remains of mastic on it.
remains