If the Factory says 4/4 then that's in error. In 1953 there were no 4/4s made, solely +4s. The only ones with single spare wheel were the 4-seaters, yours should be a 2-seater. It was sold new in the UK and had disc wheels, no wire wheels.
So, one could say it has been "modified" over the years. The P prefix is correct for the flat rad plus 4.
