According to what I could find your C5500 would have come with either a 5000 lb or 7000 lb front axle as standard equipment (see Chevy Master Parts Book extract). There were possibly other optional heavier duty axles available too.
The best way to determine which axle was installed on your truck is to locate and read your "Service Parts Identification Plate" decal that lists the equipment that was installed at the factory.
The following codes apply to your '72 C5500 to ID which front axle it has:
F43 = 9000 lb front axle (maybe optional)
F44 = 11000 lb front axle (maybe optional)
F47 = 5000 lb front axle (standard)
F48 = 7000 lb front axle (standard)
Let us know and we can try and help ID the steering components you seek to be sure to get the right ones.
