Thank you for identifying the car you are working on.
I have removed the intake manifolds from a Series III XJ6 (4.2L XK engine with Electronic Fuel Injection) about six time on my Series III XJ6s and parts cars. It has never been easy.
I have been able to remove all the nuts on the bottom front of the intake manifold by removing the air filter housing, the ignition amplifier, and the distributor cap with the spark plug wires still connected and then reaching under the manifold to remove the nuts toward the front of the engine. I removed the battery in order to remove the nuts at the rear. On at least one occassion I had to raise a car up on my lift to access one or two of the nuts that I could not otherwise reach. Putting the intake manifold back on and tightening up all the nuts is a similar hallenge.
BTW, you will probably have a challenge separating the intake manifold from the blick even after you remove all the nuts. There are lots of posts about this in the archives. I usually have to pound on the intake manifold with a heavy mallet, while protecting the manifold with a piece of wood, in order to break the paper seal between the intake manifold and the block.
Needless to say this is not an easy thing to do.