Hi Bill,
the chassis number tells me it was built in 1944. The postwar Army number, 00YY24 is not a lot of help, until I found reference to a QLT Troop Carrier with the number 00YY61, knowing how the numbering system worked I have a strong feeling yours is a QLT Trooper. This was the one with a chassis extension (extra to the part you are missing. The side tanks also indicate it could be a QLT. Proof will be if you can find the number stamped on the side of the chassis.
The contract number bears no reelvance to the original contract. Finally, Base O/H means Base Overhaul. MTRS number was the code for the workshop that did the work, not likley to have been an army base, more like a large garage or makers service depot who had a contract with the Ministry of Supply.
Hope this enlightens you!
Richard