You got me on that one! If I'm thinking right you have a shock absorber type mount in the rear. The 72 does not have this. I don't think the rear quarters are exactly the same. The bumper probably would not match up to your body lines very well.
Just remember if you fill that area wether it is with a tail pannel or just metal. And with the 72 bumper you will have to move the neck of the fuel tank down.. I have seen people put flexable hose (made for gas tanks) between the nub they left on the tank and a little bit of the original neck positioned in the new location in the middle of the bumper.