B-Body 8 3/4 in a A-Body
Yeah, its very common to put a '70 or earlier B-body axle in an A-body. I actually recommend it on a Duster/Demon/Dart Sport, or a 67-69 Barracuda Fastback...makes the tires sit better if you use the same size all around.
I used a '68 model in my car.