A picture of the lower inner corners identifies the year by the profile of the deflector. Overall
Dimensions are the same between the years on the closed cab cars.
Except for the slant window cars of 1931.
Personally I would try and make a trade for a good, sound 30-31 standard frame.
The several frames I have installed glass in were not pinholes in the glass channel, except one of the 4. Rust is not your friend.