I don't know why you would want to put Cj axles under a yj even if you could. The Dana 30 is a passenger side drop and a weaker 30 then the YJ has and the AMC 20 has weak tubes and 2 piece axles that are prone to fail. And unless you find 83 or newer they will be narrower then the YJ.
As for the springs most people do the opposite and change CJ springs out for YJ springs because YJ's have 2" front springs where as CJ's have 1.5" springs that ride extremely rough.