I have similar Curtis windows in my 1941 bungalow. They work well, but need refurbishing and I can't figure out how to remove the sashes. I've removed the parting strips, but they have an additional thin metal "draft stop" on each sash that mates with a U-shaped slot in the jams, lined with a similar metal strip.. so the sashes are still held captive in the jams. So, I can't figure out how to remove the sashes. I forced one out, since the thin metal flexes a bit, but I haven't tried putting the sash back in yet.. fearing the thin metal will get mangled. Could these be permanent "factory assembled" windows, that the sashes can't be re-installed? Does anyone know of a trick to do this? Thanks!
Just to answer my own question.. I found the secret to removing these sashes posted elsewhere (http://bobvila.com/forums/Doors_and_Windows/posts/18643).
I'm in the process of restoring these windows, and impressed by their quality and detailing. I'm quite sure, in fact, that the "draft stop" metal track and mating fins on my windows are made of stainless steel.. or something close to it. After 70 years of exposure there's not a hint of rust, and they've polished up quite nicely.