He can only use those 8 1/4” brakes if he is changing to large bolt axles, if he has small bolt axle now, that is. The 8 1/4” brakes are the same as every other large bolt brake setup, save for the shoe width, which I believe would be 2.5”.
A "B" body 8 3/4 axel assy should be large bolt pattern. Only "A" body 8 3/4 axles were small bolt pattern. Didn't all Volare/Aspen have big bolt pattern? As for swapping, I can't answer that.