Is this the right forum? Did search and all of them seemed to be in All Itens.
The Clayton wagon used a rather unusual valve gear which was replaced by Robin Dyer by Joy, with a follow up article by Bernard Lundberg suggesting using the original gear. I only have part one of his article, July 1988, so not certain if he actually made it.
Doing a search through my hoarded copies of old engineering magazines and came across an article on valve gears in the Practical Mechanic and Engineer's Magazine for 1846 page 271.
This describes it as Mr Dodds valve gear and used by Robert Stephenson on his locomotives. Only half a page with a coupe of woodcuts but undoubtedly the same method.
Bit obscure, and not mentioned by BL so might be new, worth making a note of just in case.