66 Mustang Rearend

The 67 axle carrier will fit in the earlier model provided they both have the same size ring gear. They could be 8" or 9" but are both probably 8" since they are much more common. I would see no reason to change the flange, seal or nut if it is not leaking or loose. I'm not sure about the drive shaft but it will more than likely not work as is. The length may have to be changed and maybe different u-joints used. A 6 cylinder drive shaft may be too small for a V8 then again maybe not. I'm sure somebody that has done the 6 to V8 swap will be able to answer that question.