According to my book a 1954 GMC 300-400 series which are 1 1/2 to 2 1/2 ton use a 7/8 bore and I would imagine Chev would be the same. If your truck has duel wheels, it will have larger cylinders in the rear and relatively small cylinders in front to keep the front wheels from locking up upon hard braking. The GMC number for the correct wheel cylinder for a 54 is 5454387