Here's the inside showing the storm window and crank.

Thanks, mmarse1. Yes, all of the inside window openings look like that except that some aren't painted. I think only the frame is made of wood. I'm not sure exactly what a return is. Here's a more detailed picture without the storm window.
Thanks,
Derek

Derek,

These steel casements are not what folks would qualify as a good candidate for historical preservation, retrofit.

What you want to put back in there will depend on you and your preferences.

Most casements are well engineered and getting those leaky and thermally conductive units out will make a big difference the home for you.

Thanks, windowswashington. I think replacing them is our preference but want to make sure that we don't ruin the look of the house.

Tough to duplicate that look without using steel (thin lines).

I would suggest replacing them. My tract home (built in 1957) had a metal frame casement window above the kitchen sink. It had an integrated storm window on each casement, but it still sucked out the warmth because of the metal frame. Replacing it was the best thing I did. Of course, there was no look to preserve since all the other windows in the house (outside of the bathroom) are wood double hung windows.

Maybe look at different brands of quality windows and see what comes close to the look you want??

I would suggest that you use vinyl, you will have the best high performance at the lowest cost.
You are going to be shocked at how bulky the new windows seem, you will have a net visible glass reduction, can not be avoided.
You will be so excited with the new windows that open, close, and preserve energy.

theWindowNerd...