I'm installing nice new vinyl windows, and in order to maximize the glass area, I've ordered new construction windows to avoid having to set them in the existing window boxes and live with the frames taking up more space than necessary.
However, the new windows are about an inch deeper than my current awful aluminum windows. As a result, I'm going to need to cut back the drywall in the window boxes by about an inch. It's a very cramped area and I'm not sure I'll be able to get my circular saw all the way in there. Since the lumber making up the rough opening is behind the drywall, I can't use any kind of saw that needs to penetrate through the other side by more than half an inch, if even that.
What's the right tool for this job?