My roommate just recently bought an old school building that was built in 1922. We need to replace the single pained aluminum windows with the new vinyl windows that the previous owner purchased. The problem I am running into is there is no wood at all around the current windows. It's all masonry. The windows are only being held in by a mortar. The existing window measures 75"x39" and the new windows measure 74"x37 1/2". What is the best way to install the new windows? I also have to replace the lentils above the windows so should I frame build a new frame for the windows to sit in? Also, would it be a good idea to putting flashing around the sill to help weatherproof? There are 8 of these windows to do in what is going to be our living room. I am waiting for my camera to charge so that I can post pictures of the existing windows and the replacement windows that the previous owner bought. Any help would be greatly appreciated. My roommate is trying to save as much money as he can on this project. I have a construction background and am currently laid off that is why I moved in. This building is a big project and in the long run both of us will greatly benefit if we get this to work. Any help would be greatly appreciated.