All over the internet there are methods about the differential crossbeam cushion removal. Experiences varied from "no problem" to "it took me a week." Today was my turn.
After the tabs were bent back up, and the cushions soaked with PB Blaster, the first one was out after no more than 10 strikes with a 4lb sledge onto a junk socket placed in the cup. The second one, not so much unfortunately.
Soaking, torching, more hammer strikes and nothing. It would not budge. I had to assume that the rust issue that I had discovered in the sombrero had also affected the cushion. So after some headscratching, I rigged this tool up and it worked effortlessly, without the need for a huge press or drilling or anything else super involved.
Get a 2 claw gear puller, a junk socket and a bolt with a head large enough stay on top of the socket.
These pictures are after I already had both cushions out, so you'll have to just imagine that the cushion is actually all the way up in the hole of the crossbeam.
Hope this helps. I didn't see this type of solution anywhere online. C3 restoration will test your skills, test your patience and certainly make you a better garage mechanic. Remember, they are simple cars over all, but they are old!