Everything, as a complete assembly, should bolt in.
We need pics to determine why the '71 parts you ordered don't fit (Disc? Drum? Small bolt pattern? Large bolt pattern?)- my guess is that the previous owner did a disc brake swap to the '71 that used '73 and up parts, or you ordered drum ball joints for your disc suspension (or vice/versa)- but we need pics to give you a solid answer as to what you actually have, and what you need to do to make it work.