[Lynn Eades]

Malcolm, I have not yet done this, but I make the following suggestion,
remove all of the engine cover assembly. (this depends on your answers to the following questions)

You are going in, presumably because you have a valve problem (stuck or burned?) You suggested this.
Have you thought about a blown head gasket? (between two adjacent cylinders?)
A compression test indicated a low or no compression?
You then repeated the test with a little oil in the cylinders to seal the rings?
If nothing changed, then you have a valve problem?
If the compressions went up you have a ring problem.
If you have a ring problem, then it's an engine out job anyhow.

Before you do any more can you give us a bit of a back ground?
If the rings are stuck (or a valve) because the engine has sat a long time, then they might free up with use.
If you know the history and the engine has become tired you might end up with a big job on your hands.
Going back to the start of my circle, If you remove the whole cover, it will give you reasonable access to do the job , along with that it gives you the opportunity to tidy up other areas that might need dealing to. Valves that have not been out for a while can be hard to remove, so you will need all the room to do a good job. At the very least you need some room to just clean up the block face, for a new gasket. This is hard enough working around the studs, without all the other stuff being in the way.
Have I convinced you yet?
Tell us a bit more.