Look for 73 and up 7 1/4 with 10" brakes, everything bolts right on if you use Dr. Diff's axles.
They are the same. I had a 7.25 in my duster when I bought it. I installed a factory hemi car Dana and moved all the rear brakes over and everything fit perfectly.
Not all 7 1/4 backing plates will work. I have a 75 Dart in the shop right now with a SBP 7.25 and they are different.
I think the newer 7 1/4 BBP backing plates are the same but many of the early 7.25s have a 4 bolt pattern that's different than the five hole pattern (you can't just drill a hole). Also, the offset difference that's a problem on the SBP 8 3/4 A body rear may be an issue on early 7.25s as well.
I have a correct set on Ebay:
http://www.ebay.com/itm/33096658105...X:IT&_trksid=p3984.m1558.l2649#ht_3229wt_1119
You are correct the only difference is the missing lower center hole which can be drilled or just remove the stud in the housing.
I have actually had 60's 7 1/4s where the four holes had a totally different "x" pattern. It would be necessary to drill all five holes on that style.
No, it was a small bolt. and the backing plates were way off.
To summarize all of this: The later model LARGE bolt pattern 7 1/4 rear backing plates will work. Sometimes you have to drill the extra hole but I've actually had some that had the 5th hole in it. The small bolt pattern 7 1/4s are not likely to work. All 8 1/4, 8 3/4 (non A body), 9 1/4 and 9 3/4 (dana) and 4 1/2 BP truck brakes should work as well. It's not a hard set of brakes to find!