Tubby,
There's a Production List page on this site
http://www.bac1-11jet.co.uk/
You are correct that all 1-11s had both a 3 digit Type number and a two letter type code that was on all wiring diagrams (plus slash numbers if there was more than one mod level for the type or latterly a letter code if it had been mod'd for another operator e.g EK/D for the Robin Loh conversion from Channel.
The list gives Air Malawi as taking delivery of one Type 481FW (243 7Q-YKF). I remember working on an "Engine Contingency Rating" system for Hot & High ops that allowed the crew to exceed normal ITT up to (if memory serves - it's a long time ago) 5 times per engine before a full inspection.