My house in El Paso, TExas is a brick veneer with casement windows,
built in 1959. I'd love to replace those drafty single-pane windows
with good energy-efficient double panes. I could probably do the job
myself "IF" I knew how the present windows were installed. And "IF" I
don't have to take bricks loose on the outside of the house

In that era, were the windows usually installed from the inside, with
large screws going through the sides and into the framing of the window
opening, which was then hidden by the drywall in the window opening?
Or were they installed from the outside and secured with a nailing
flange on the outside of the framing, which was then covered with one
row of bricks?