Thanks everyone. I have done a little research of my own and it appears that ZL and LC are indeed sister ships. I haven't been able to find out anything about ZR so I shall agree with David on the Ghana Airways angle. However I have looked at pictures of all three aircraft today and they all sport an extra cabin window fore of the wing. ZL was pictured next to a BA type 806 so the comparison was easy. So these aircraft have either been modified to allow the extra window or there is a fuselage plug.
All of these Viscounts passed through Leeds Bradford during the late 70s/early 80s. I miss those days. Great aeroplanes.
By the way I Southern International may have had their hands on BBDK at one time. Or CSZB. Both went through Field's/ABC/Dan-Air as well I think.
Most of the BMA fleet was ex-SAA but they also had a few ex-Lufthansa machines, via Nora Air.