Does anybody know the difference between the two years and why you cant interchange them? Has anybody ever modified a 71 rear valance to fit on a 72?

I ask because i could really use i new one, as ive got two in rough condition. Now, AMD makes a brand new one for the 71, but not for my 72 RR. Besides the bumpers being obviously different, i cant imagine they are that far off of eachother. Its gotta be the same width because the quaters are the same right?

If anyone else has been down this road, please fill me in haha. THANX!!