G'day Folks
If the body is removable I would suggest that the Chassis Number would be under there, as on some of the No5's, so that is where I would look,and then restamp the No in a place that Civilian Transport Dept's can see it, a complete and exact copy. or you could end up with one of those 18 digit specials and it listed as "Homebuilt"
cheers
BTW those brake shoes look very similar to common cars rear drum brakes,find the earliest date of manufacture of the trailers, and then X reference the shoes to common car/utility rear shoes. or Caravan builders. the AYG 8108 is a Series 3 wheel part No possibly a 6.00 x16 but was interchangable with Perenties. check by looking in the centre interior of the wheel where it is rivited.
cheers