Whats the best way to arch a square opening using drywall? I have a 50 year old house that has plaster finished walls on top of what looks like 2' wide gypsum board strips. (No wood or metal lathe) The entire finished wall is 7/8" thick. The opening is 7' wide and approximately 7' high and I would like to just "curve" each corner to provide an overall archway effect. I am decent at working with drywall, corners, taping, etc. but have never added drywall to curved surfaces. Please help!