2wd to 4x4 conversion

[MYBAD66]

So I have a 66 C20 with a 305. But I'd really like to have a 4x4 personally, and looking at 4x4 trucks in my year they're all pretty uh out of my price range. So I was wondering what parts I would need to convert my 2wd into a 4x4 truck and where I might need to get them. Are parts interchangeable between years where I could find a donor 4x4 of a later year that I could use? Or do I need to find my exact year range? Or is this gonna be harder than I thought and would have better luck converting over to a later year everything? Tips and tricks are always helpful. Thanks forum!