Rubber bushings will work, but I don’t recommend them. Rubber bushings are the traditional choice for throttle linkages dating from the days when a throttle linkage included a shaft that fit a bushing on the firewall at one end and a bushing on the engine at the other. The pedal was connected to a crank near the firewall end and a link to the carburetor was connected to a crank near the other end. With such a setup, the engine could bounce around on its rubber mounts without affecting the throttle position.
The XJ-S does NOT have such a throttle linkage; it uses a cable to connect the pedal on the firewall to the engine. The throttle linkage bushings in question are for a shaft that is securely mounted to the engine at both ends, there is no relative movement and hence no need for them to be rubber. And, of course, as bushing material, rubber is – well, it’s not optimum. Hard plastic or nylon would be better. Sintered bronze would be better. Pretty much any rational material choice would be better. And better is more important than you might think, as having minimal “stiction” in a throttle linkage is a good thing when driving.
Why did Jaguar use a rubber bushing here? Because somebody involved wasn’t thinking. It’s a mistake, pure and simple.
And yeah, replacing the bushing without disassembling the bracket from the back of the intake manifold is difficult. If you can chuck up your new bushing in a drill or lathe, cut a groove around it, slip it in from behind and snap a clip onto it, great. If not, just go ahead and take the bracket off. Then it’s EASY to install the flanged bronze bushing in the photo above, just slip it in and bolt it back together.