II believe that in 1946 the ID plate was attached to the truck by screws. I do not know what style of screws were used. Early AD truck ID plates were attached by special clutch head screws.
How was your ID plate attached when you took it off? If they are original, and you have a reasonable assumption that the ID plate belongs to this truck, I see no reason why you cannot put that plate back on the truck with those correct screws and avoid any legal trouble.
