Oswald- Isn't your truck a '54 3600? The '51 fuel pump has the same output rate/psi as the one listed for 1955.2 Series engines, so it will work as far as performance, as well as fitting in your engine compartment as your '54 mount setup won't interfere with the fuel line plumbing.
If your truck was plumbed for the later style pump mentioned by Jerry, it's not that hard to change your fuel line layout to work with the earlier pump ports.
