I have a brick ranch house made in the mid 50's. My dad and I came across what I believe to be the same problem. Our solution was to build the frame for the new replacement vinyl windows ourselves. We just got pressure treated decking 2X4's. We had to rip them down to 2X3's so they would fit between the drywall and the brick. Note: You may need to get a smaller window, but in our case they fit like a glove. Also, get some insulation to stuff behind the ripped pressure treated 2X3's. After installing the window just add some vinyl trim around the outside and inside then caulk it up. More, we had to make new window sills in my case, because the old sill were made of tile and some broke when removing the old aluminum frame via crowbar :-) I hope this helps.