Bay window drapes 30&40's style??

I would definitely try the clip on rings! I've used them several times and they really work great - you can also fold the curtain to make it shorter with the clip on rings too,

I would try the rings and then fold up and pin the excess length to gauge it before cutting.

Could you hang the bar across the whole bay window and have them open on either side against the walls. ie beside the bay not inside it.

Lowes has bay window curtain rods have you checked those out?

https://www.lowes.com/pl/Bay-window-curtain-rod--Curtain-rods-Curtain-rods-hardware-Window-treatments-Home-decor/4294398487?refinement=72151205

I would suggest using the rings and having much of the trim showing on the bay window.

Also, let the fabric of the drapes hang full length until you decide the best look for the window decor.

I would use the clip-on rings. Let them hang before you cut, as you know, there's no going back once you do cut them! Great find!

I believe you are looking for a Art Deco look. Heres a page with some pics that may help you out

https://www.google.com/search?q=art+deco+drapery&tbm=isch&ved=2ahUKEwiFobntnqTxAhUJOK0KHXHqBPgQ2-cCegQIABAA&oq=art+deco+drapery&gs_lcp=CgNpbWcQA1AAWABg1bEIaABwAHgAgAEAiAEAkgEAmAEAqgELZ3dzLXdpei1pbWc&sclient=img&ei=6yvOYMX_LonwtAXx1JPADw&bih=757&biw=1600

I had the same problem in a bedroom window. I actually put up tension rods and hung from inside top of window. I tried the rings but I did not like that look.

First get a tension rod and hang the curtains and you will need 2 tie backs then after the curtains are tied back pull the fabric out so it hangs over the tie back and puff it then do other side pull enough so curtains are not that long