SP2482 would be for a 0.812 (13/16) inch bore size, which I thought you mentioned it was, SP2485 is for the same design master cylinder but 0.875 (7/8) inch bore.
Did you manage to get the other catalogues and the illustrations catalogue that diagram came from?
Caribougone's leaflet is excellent too, showing separating the bottle, otherwise absolutely forbidden, what I don't have is part number data for the circlip or bottle seal, which seal I imagine might be like a used piece of black chewing gum by now. Similar tandem master-cylinders abound, often with remote twin outlet or paired reservoirs, you need to watch though for correct orientation of the mounting flange, horizontal in this case, I think, not vertical. Modern bolt on replacements from the likes of Wilwood might be suitable.
I had looked into this back in 2016-2017, with a view to changing my servo-ed 0.812 single circuit system to tandem, split front-rear, but chronic more pressing bodywork issues, still ongoing, intervened. Not helped by having a spare brand new 0.812 master-cylinder and a few SP 2381 service kits for that master cylinder laid in.
Had thought a Ford AV0 rs2000 mk1 Escort type suitable, as it bolts to the same Girling Servo in that application. Also possibly some post-77 MGB/MGBGT cars might be similar but do not know the bore sizes of these BL or the Ford ones, to know if they're truly compatible. I really needed someone else to do this first, as an unwitting guinea-pig/test-pilot, rather than obtain parts on a trial and error basis, but I'm sure suppliers could provide further data on their wares to aid in a decision.