Cheers guys,
Andrew, thanks for the info, I should have been more precise but I was looking at using the 3.5mm jack output on the rear of the CB (or indeed a feed straight from the speaker) into the Clansman harness rather than modifying the CB mic plug/socket.
00EC25, thanks for the info. Any chance you could check that pin-out for me when convenient :-)? If I plug the CB into 'A set' on the IB3, will I get it through both ears or just one, and will it come through all headsets on the system? (Not very familiar with how all this works beyond very basic use as an intercom.)