Thanks for the replies. However, my Rayburn (and I assume all others) was delivered with the bricks installed, ready to fire up. The Rayburn installation manual simply says:

The firebricks fitted to Rayburn Cookers are of first
quality manufacture, and providing the cooker has been
installed and used correctly will have a reasonable life.
They are, however, expendable items and in time will
require renewal.
The renewal of firebricks is not a major operation and
can be carried out by the average person.

As I hopefully qualify as an average person, I suppose I should just order the bricks and cement and go for it. I was just hoping somewhere there was a little information so I could go into the job knowing what was going to happen rather than having to figure out each step as I went along. Past experience tells me that kind of on-the-job training often ends up with the first job teaching me a lot while ending up with a less than perfect result. But if that's how it needs to be, so be it.