Terry
The number plate transfer, right or wrong, will have been applied at the factory. I certainly would not remove it from such a pristine model as you have.
Here is my 813 155mm gun showing its tricolour and number plate:

I have owned this from brand new, I bought it in Celle, Germany when I was serving there in 1971 and I can verify its authenticity.
Dave
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616-AEC with Chieftain Tank
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-073 Land Rover, Horse Box and Horse (1960-67)
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-073 Land Rover, Horse Box and Horse (1960-67)
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-105c and 383 4-Wheel Hand Truck (1949-1958)
-105c and 383 4-Wheel Hand Truck (1949-1958)
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--22c Motor Truck (1933-50)
--22c Motor Truck (1933-50)
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Trailer Caravans
Trailer Caravans
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