hi Stef,
This is not specifically a REME plate, it is a Ministry of Supply data plate and I believe that both workshop numbers on the plate are what is known as AAW, Army Auxiliary Workshops, in other words, contractors. These were often main dealers, garages, manufacturers service depots, etc. The post war number can be cross checked on what is known as a Key Card and could give a wartime number. The R in the registration number means it is a rebuild and therefore could be a mixed up vehicle and not totally original. I notice another couple of holes drilled in the side of the plate, where screws have been in the past, but no holes in the bodywork. This could mean it has been removed on a rebuild previously and changed over.
The army number might be found in the Key Card for that batch of numbers is still available, either Wally Dugan on this forum or the Royal Logistics Corps Museum at Deepcut may be able to help.