I have the axle off mine now. I placed a 6-ton bottle jack with pieces of 4x4 between the extension legs and then kept spraying PB Blaster down around the extensions while rapping the mian pipe with a hammer to break up the rust. It took three days but it finally let loose and I was able to use the jack and pop the rt. extension out. Cleaned it up good inside and out, lubed it, slid it back in and pinned it, then jacked the other side out. It took some time but the process didn't damage any parts.
The harder part for me was cleaning the main and extension pipes inside and out. I used electrolysis to de-rust the parts. Next I took a 2-foot long piece of 5/8" round stock and cut threads on one side with a die. Also cut threads into the stud of a wire cup that just fit into the main axle tube. Used two nuts to lock the two pieces together and then used my drill to wire brush the insides clean. Finally I treated it with metal prep to keep it from rusting back. If you can sandblast everything, that would certainly be easier.
I'll probably epoxy primer the outside of the extensions but as noted eariler, the fit is tight and I think that most of the paint will be knocked off during re-assembly. I plan to use a generous amount of never-seize as well.