I've built several of these windows, the T3 temper is going to be a bear to get the outer fold without cracking.
I used 3003, it polishes up pretty good, the slight color difference isn't noticeable since its a standalone piece and just a narrow ring around the glass.
Vintage trailer supply has the extrusions that go vertical up the window and the cranks slide in. The steel pieces that hold the openers isn't too bad to replicate except making the slot. A hand grinder with a cut off wheel will work if you don't have a mill.
The bend sequence is pretty critical so you don't work yourself into a corner.
A miss step with a polisher will have you starting over...