Can anyone with a Graflex SLR sheet holder measure or tell me what the distance from the frame of the holder to the film surface is?

I'm trying to construct a back for my 4x5 R B series D out of a Polaroid pack film back from a Vivitar slide printer and a piece of quality birch plywood. It wouldn't have a dark slide, but I could remove it in a changing bag if I ever really need to remove it before the pack is used up.

For what it's worth:
Graflex style Rollfilm holder face to film plane is 3/16 inch.

Regards,
Dave