Bonny,
That is a '54-'59 base.
Leighton's covers are first class, I have used several. You also need the two rectangular rubber blocks which fit in the apertures on the front quarter and support on the frame rails.
Measure the base before you order a cover to ensure it is the correct length. [Don't ask why, I am still not happy about some pattern bases I had.]
A bit of trivia, there is no piping on the cover for those years.
Trev.