Denis Welch &, AH Spares sell the adapter plates for mounting calipers on the older-style swivel axles. You can get them in the wider bolt pattern to fit the later Type 16 Girlings, 4-piston Girlings or 4-piston Toyota calipers.
The Moss catalog makes it look like the kingpin is the same throughout. My BJ8 swivel axles fit onto my BN6 kingpins no problem.
The main thing would be acquiring disc rotor-compatible disc wheel hubs from BT7/BN7 onward.
I believe there's an older post in the archives where Randy discusses what he went through for the conversion.