Newer vs. older D60
As for the swappnig the whole axle in thing - it's a pain to do if the axle is 80+ and your truck is a 70's or earlier truck. The pumpkin if moved out towards the knuckle more on the later trucks and since the spring perch is built into the pumpkin this makes putting a newer axle on an older truck a bit tricky unless you go to a coilover and radius arm or 4 link style front suspension.
As a quick reference to show you what I mean here are a few pics of an 80's D60 alongside a 78/79 d60. Notice the pumpkin is closer to the end of the axle on the newer axle.







