I'm not a Graflex expert, or indeed novice, but I read : Fit a back adapted for 4x5 (assuming your graflex has the graflok back system, not the standard ground glass spring back) then an appropriate 4x5 digital back adapter.
The Super Graphic-Super Speed Graphic has a Graflok/International back therefore any digital back made for 4x5 Graflok/International back will work.