what are they talking about as far as outside measurements i need 5ft from inner drums the b bodies are 60 to 63 inch but is that from the ouside of the drums
They are talking about the distance between the wheel mounting surfaces. The distance between the backing plates is not an accurate way to measure since brake setups differ between applications as well as accounting for wheel size, width, backspacing, etc.
B.E.D is right, the backing plate to backing plate measurement is meaningless. Go by wheel mounting surface to wheel mounting surface.
The only way to get the right rear end is to put the tires and wheels you are going to run in place where they clear and look good, then measure the spot where the brake drum touches the wheel on one side to the same spot on the other side.