isaacc7, a thought;
a 4x5 Speed/ Crown graphic body is almost the same size as a 5x7 holder. If you duplicate the body with 3/8" side panels and 3/4" top & bottom it works out. Make the interior the exact same size as the original and take exact patterns for the screw holes. At the rear a piece of 1" aluminium angle stock at the bottom and 2 turn screws at the top hold the holder/GG. You can synch the rangefinder to the film/lens and use the sports finder at the front. All told about a weekend to finish.
Good luck with it.