One of my weekend jobs involves working at the local vet clinic as a handyman and fixing up the old horse barn. This window location is original to the structure but was cut out in the 70s to add a massive air conditioner.
I had to reframe the section of wall and we decided to go with a big box vinyl window replacement that I finally cased over the weekend. The cap flashing is my favorite bit.
All it needs now is a little oil-based primer and some paint to last another 50 years.