I think the NAA series is MT801. (ie 'Melbourne Temporary 801), not 810.
At the time indicated by the Test Instruction (TI) numbers, the title of Monegeeta was: Department of Supply, Design and Inspection Branch, Design Establishment, Trials and Proving Wing, Monegeeta. It was not part of the Australian Army, but the Dept of Supply. The name does tend to alter a bit during the late 40s and 1950s, but the essential thing is that it was Dept of Supply, with Army personnel on posting.
During the war years, it was Dept of the Army, Master General of the Ordnance Design Division, Mechanization Experimental Establishment (MGO MEE), then later (immediate post war) it is referred to as the Dept of Supply, Army Branch, Trials and Proving Wing, Technical Services Establishment (when the TIs were in the 1400s and low 1500s).
'X' was simply the sub-unit tactical sign of a trials vehicle while assigned to T&PW, Monegeeta or at Maribyrnong, or at TTU, or whereever. It possibly does stand for 'experimental', but I've not seen anything official to support that, and tend to think it was simply a unique and obvious marking to indicate a test vehicle. The Brits appear to have used a stylized 'T' (test or trial, perhaps?)
When/if issued to Army for Troop Trials, the vehicle was given a Unit sign/sub-unit tactical sign corresponding with the Unit concerned/conducting the trials. By the time of the L/R 110, the Dept of Supply were long gone, and the testing was all done by Army, hence I'd suggest the use of unit signs and sub-unit tactical markings on the trials vehicles.
NAA no longer photocopy: they scan, and at a resolution too low for reasonable reproduction in print. If you request and pay for a copy online, the report and the images within the report will be made available to all on line, and the images could be 'lifted' from there for screen display if desired. Most of the reports you refer to were opened pre-scanning/pre-digital era (in the 80s and 90s), so if you want a scanned copy up on line in Recordsearch, it has to be paid for. Current rate is about $20 a file, so it can get pretty expensive pretty quickly, I can assure you! There are currently 1026 reports listed under MT801/1, but only 6 are digitized and available on line, including TI1762: the 1/4 ton truck trials of 1958 (M38A1, Willys jeep, Land Rover Series 2, etc)
Mike C