A Body Disc Brake help

I just went over and looked at duster, I took a back wheel off my brothers 66 fury 3 which I know is a big bolt pattern and it fit perfect on front of duster, but I was reading that the big bolt pattern was from 73-76 could this be cause the car was made 9/72 ..? Would I need to use the bottom aarm on switch over ..?. Thanks all for the input