Another 5-lug conversion question from a newbee

[1970SWB]

I've been "lurking" on this board for awhile and finally picked up a '70 SWB (2wd) pickup, & now I have some questions, first I want to convert from 6-lug to 5-lug, I have the front suspension from a '73 pickup, and plan on changing all the A-frames (for the rubber suspension bushings) and of course disc brakes, I also have a complete rear axle from a '72 SWB pickup, should I change the entire rear axle or can I just swap axle shafts? Some posts on here are talking about different length axles for different years? Thanks for any insight on this & I'm sure there will be more questions to come.