I would sound out the RTA on the subject - but note that my 1970 ute is described on the registration as a TT - which it turns out means tabletop. When I attempted to correct this I was advised by the RTA that in 1970 this was the only body type made by Landrover on 109s. It apparently was described as a TT when inspected by the RTA when I transferred it from Victoria.
I think that in theory vehicle bodies can only be built by licenced body builders, and any exceptions require an engineer's certificate, but this may not apply to vehicles built before the ADRs existed, which would apply to your Series 2.
There is no way that they are going to know that the tray is not one that was fitted before these rules existed (unless you tell them), so assuming that it fits the rules at least approximately, I doubt that any questions would be asked. It should be of sensible dimensions and construction, no sharp edges, have mudguards that look as if they will stay there, and have either the original lights or ones that are certified to meet ADRs.
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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