Hi Michael
At one time in the late 70’s or early 80’s at a guess there were castings, not sure about drawings, available from George Wainwright for his own version of the Crab in 5″. I know he certainly completed and ran his own model from castings from his own patterns, can’t remember if it was slide or piston valves, I remember seeing it at a rally and later was pictured in M.E.
I’m sure that Mr Wainwright also marketed castings and drawings for some wagons in 5″. I’m sure the name is right but it was a long time ago! Might give you a basis for some searching.
Dave
Something has just stirred in my addled brain that the wagon designs were taken over by Doug Hewson, but I may have made that up!