you have two choices make a freedom of information request to the MOD at cio-foi@mod.uk giving as much information
as you have mainly the army reg number this cost nothing secondly contact the RLC MUSEUM DEEPCUT CAMBERLY SURREY
they have a charge of £35 if you have not looked for the army reg number it is found on the near side chassis rail near to the cab it should look like 05 BM 85 or such on a square plate
REGARDS WALLY