I have replacement vinyl windows that were installed in, what I believe to be, the original metal frames. My house was built in 1955 and what I think is the frame is a hollow, tubular metal that is 1" thick. The frame protrudes past the surrounding drywall around some parts of the frame but the metal stool protrudes approximately 3/8" all the way across the bottom of the window. Given this, how can I install standard window casing? Pictures of what I'm referring to are attached.
I'm at a loss for what to do so any recommendations will be greatly appreciated.