@oliton let me know exactly what you want to achieve & I'll have a look at my Beseler 45cb7 with both 504 generations of holders this evening - I don't think either will work because the Beseler is reliant on location pins under the carrier, whereas De Vere use location stops on the chassis. If you really want the De Vere carrier experience, I'd strongly recommend actually just getting a 504 - it is vastly better than the Beseler in design, build, durability, ergonomics.
Edit: Have now investigated the practicalities - the 1908 carrier is too fat to fit the gap in the Beseler chassis, the 1978 will fit. The problem remains that of accurate location - and unless you can fit the location pins needed by the Beseler chassis you'll be spending a lot of time aligning things. I do have a plan somewhere that I drew up from a scanned 1978 with the intention of making a fixed opening size sandwich carrier (De Vere made something not dissimilar - some customers only enlarged one or two formats & had no need for a universal carrier - and it is very convenient not to have to change inserts routinely).
As you seem to be implying that what you find most troublesome about the Beseler is the single size carriers, you might want to investigate getting a universal glass Beseler carrier & removing the glass, then getting some inserts cut for that. It wouldn't be very difficult for a reasonably skilled maker/ metalworker & they could be quite readily water cut.