Puttinalong,
If you have the original 1954 1/2-ton enclosed driveshaft (torque tube) rear end, it has a 3.90:1 ratio ('47.5-'53 half tons had 4.11:1 ratio).
If you go with the Patrick's 3.55 you will see (feel?) about a 10% improvement.
Jim Carter's website has a Technical Article on higher-speed (lower ratio) drive lines.
http://www.oldchevytrucks.com/cgi-bin/htmlos.cgi/001269.1.928549743537045705 The Stovebolt Page also has a technical Article on this subject:
http://www.stovebolt.com/techtips/torque_tube_swap.htm This is probably the most often asked question by owners of 1/2 ton Advance Design trucks (along with questions about carburetors, electrical systems, king pins, tires/wheels, braking systems, paint codes, parts sources, ID codes, etc, etc). Welcome to the forum.
Good luck,
Tim
