Thanks for the info! I’ve learned a lot this morning. I had not heard of the Motors auto repair manual, I’m going to buy one. I read the old thread, I’m going to take Kube’s advice there and do the whole job, not use a quick-fix seal. He says it’s not that hard…
And I found the section in my green “shop manual / service handbook”. It says the differential gear is forged onto the axle without a spline, so good thing I didn’t try to remove the axle with a slide hammer

It also says “As considerable special equipment is required for disassembling and reassembling rear axles, it is recommended repairs should be performed only by competent repair men having the necessary equipment.”
Well, Ford38V8 says I just need to know what a box end wrench is, and my wife bought me a coffee mug that says, “Ready, willing and vaguely competent”, so I think I’m ready to go! Haha, this must be why I bought an old car.