belltech 3120 drop spindles

[TruAggression]

Ok so I have a set of these 3" drop spindles part number 3120 which is for the 71-72 and searched but dont really have a clear answer yet....So I have an 87 and these are for a 71-72 which is still same stuff basically.... How do I get these to fit my truck???? I already need ball joints and tie rods so I'm prepared to get that stuff just wanna know which stuff to buy for a 71-72 or for 73-87 stuff? clear answer would help from someone thanks...