I did the measurements. although they look quite different from the outside, the inner cast of the "cone" is about the same. the 4x5 is just a piece of cast metal and a spring for the holder. I put both bodies face down on the table to measure, so measuring starts from the outmost rim. from the rim to the holder plane it's 98mm. the holder adds another 2mm which makes it 100mm to the film plane. the back opening of the cone is approx. 119x95mm.
the pack 100 body has a smaller frame screwed onto the cast cone. before the frame it's the same as above, the frame reduces it to 105x82mm. with an empty cartridge front put into it, I measured 103mm from the outmost rim to the film plane. if you would take off the pack 100 frame you'll probably already be there.
I add 2 photos. please feel free to ask further questions.
both bodies on the table
both bodies from the outside