K-36 and K-37 cab roof vent cover?

I'm still working on my new model of K-36 #489, and keep finding details that I can add here and there.

Looking to photos of 489, and most other K-36 and K-37 locomotives, I've noticed that the cab roof vent has what looks to be a smoke deflector over it.

I'm making one for my model out of thin plastic and have a few questions about them.

1: Does anyone know what the purpose of this cover was for?

2: Was there a particular era when these started being used?

3: Are there close up photos of these in any books?

4: It appears they are supported in the middle by small rods. Were these rectangular or circular rod?

The cover I'm talking about looks like this:


Matt
Lake Forest, CA
Click Here for my model train photo website