It is not the wideness alone that counts for the so called International Graflex 23 coupling system, nor the total thickness of the cassette.
The shape of the longitudinal side is at least as important. There should be a slot, a long grove actually, in it, and a screw in the middle.
In that slot the sliding thongs, the chrome tongs with the red handels shown in my previously shown photo, mus fit.
The linhof ones do not attach the same way, as these are made to be slid beween the spring held ground glass frame and the camera's backside, just like a traditional 4"x5" sheet film holder.
In the photos I attach now, you can see the shape of the camera side of a roll film cassette {a WISTA 6x9, which has the same pattern as the Horseman, the Graflex 23 and the Linhof Rollex (as used on the ALPA camera's)}.
In the first photo, if you look closely, you can see that grove with the chrome screw halfway of it, which is meant to position the cassette in the camera's 6x9 frame.
In the second photo you can see the inner side of the grove with the screws.
In the third photo you can see the traces made by the thongs when slid in that grove (a Wista cassette).
The thickness of the outer, camera oriented, side and the border of the grove is around 4 mm, the deepness of that grove is about the same.
The roll film- and the sheet film cassette must always be positioned with the dark slide upside, or on the right side when used horizontally.
This coupling system is nowadays still used on the still made Silvestri-, the ALPA SWISS- and the Alvandi cameras, and perhaps others too.
I think, but I am not certain, that the sheet- and cut film cassettes for the 6x9 Mamiya Press have the right shape/thickness.
By way of information: there is an considerabel difference between SHEET film (was plate film) and CUT film.
Sheets are 6,5 cm wide, and come as such (9 cm long) boxed by the manufacturers like ILFOR and MACO and, for the Imperial measure fans, is exactly 2,56"x3,54".
Cut film is 6 cm wide as it is a 9 cm long piece that has to be cut off a 120 roll film or a traditional sheet film (a quarter of a plate???) a not so easy DIY job I think.
BTW, I must admit never to have seen nor held these sheet-/cut film cassettes in real, what I tell here is purely based on literature, user manuals, pictures and the experience with roll film cassettes (which I use on my Silvestri, hence the photos).
PS: I am looking for a pair of SHEET film cassettes...