Anthony,
I am certain you are correct in saying it should have twin wheels all around. As it stands now the wheels are offset from the hubs, not good practise for load bearing. Looking at a list of military trailers, dated 1969, there is one listed that fits the bill ;
Maker; Dyson
Vehicle Code Number; 3488.0325
Designation; Trailer, flat platform, 35 ton, 8 twin wheels
Royal Navy
I have seen artillery radar systems built on trailers like this but could not see any listed with that wheel configuration, but I am inclined to think it might have been for equipment such as this because of the legs fitted on the corner, assume there is one at each corner?