Well have no experience with X-ray film, nor 8x10, and the thickness of the film.
Background:.
We have gotten into shooting J.Lanes Dry plates. Have an old 9x12 folder that has the correct film holders, that will take the glass or regular film, and so decided to use the same size for three different camera's, One size dry plate then will fit all the others! Converted a Zeiss film pack adapter that slid into the slots of the 9x12 folder for the 3x4 speed, and now converting a 4x5 film pack adapter for my 4x5 speed. But the right on focus location point, for the 4x5 adaption, is right at the front, inside edge of the holder. That's why we need a thin surface, to hold the 9 x12 glass plate, against the cardboard backing, while not allowing it to fall into the camera itself. . But the surface has to be thin, to keep the focal distance correct. Hopefully, a sheet of film will accomplish this.