RE: 1990 XJS radio removal
Pull both climate control knobs, straight off, use a 90 degree seal pick if they're tight.
Underneath each is a barrel nut, there is a factory tool to loosen them but if you dig through your selection of needle nose pliers/ snap ring pliers you can find something that will work.
Carefully remove the climate control faceplate, use the 90 degree seal pick in the lower slot and at the corners to pull it loose. It's stuck, there is nothing else securing it to the console.
Don't cut or break the six black fiber optic strands to the panel, just lay it flat out of your way.
The radio chassis is retained by four plastic rivets: push the centers in, then you can pull the plastic rivets...and the radio chassis... out of the cenrer console.
For reassembly, get some 1/8 aluminum pop rivets. Knock the rivet heads off of the nails, and use the rivet heads to push into the centers of the plastic rivets to expand them when reinstalled.