On investigation (and for the benefit of posterity) although the Abbot "D" Box has a twelve pin connector, it is fed by a six-core cable and only four of those cores are actually connected. Looking at the Clansman harness pinout I think I can get a CB2 working on intercom only with six cores (Pins C, D, E, M, P & S) so I've changed the connector for a normal Clansman harness plug. Not the easiest thing to do in a very confined space with little slack on the cable!
Andy