Hi Andrew,
The back is new for me. It came with a Graflex XLSW I picked up recently.
From what I can tell, both the internals and externals are intended for 6x7.
What I didn't mention, because I did not realize it might be related, is that I did not load the film properly. I did not advance it enough to start and shot the first few frames on the paper instead of film.
I'm being told now that would affect spacing. So I'm hopeful that the second roll (being processed) will give better results. I think I loaded that one correctly.
The overlap was not constant, but I don't remember if it got better or worse as it went along.