If the front are the same as 1/2-ton your front axle has been changed. Or maybe you have a 1/2-ton truck with a 3/4-ton rear axle. At any rate, you need to be sure what you have. That may be a later 3/4 ton axle in the rear.
1/2 tons and 3/4 tons of the Huck brake era shared the same 11" front brakes. The drums are the same except for the lug pattern and the hole size for the hub. I'm guessing that's what he means by that.
