I am ready to install a window jamb into my basement window now that I have the sheetrock finished. I am having an issue though where the distance from the window to the sheetrock varies around the frame, anywhere from 8" to 8 1/2". I want the jamb to be flush with the sheetrock, so how is this accomplished? Is leaving a gap in the rear against the window and simply caulking it ok? Or is there something I am missing here? Is there a tool I could use to shave the front down level with the sheetrock and not make it look like a 3 year old did it?