Bruce,
You can buy the gears from a vendor like Jim Carter or just go direct to Patrick's. Warning: they aren't cheap, and, if you have a garage do the install, that won't be cheap either. On a '54 I believe you need the spool out of a '47 -'53 diff. If your drive line is still stock you have a 3:90.1 The 3:55.1 isn't going to be that big of a difference for the $$$ you're going to spend. (this coming from a purist who would never advocate hacking up the drivetrain)!
Do you run 16" wheels and tires on your truck? If not I'd strongly advocate running 215/16 radials. they are a tall narrow 16" tire that looks great, will fit the stock rim, and will be a little taller that the stock 6.00/16.
Stingray
