Hello Tony,
Henry Greenly did a design for the GNR 8' Single in 2.5" gauge which would probably date back to the thirties. We do have a copy of the drawing for it (L78) but it is only a single sheet general arrangemant drawing, as were a lot of HG's drawings.
If the number is original, I doubt that it would be a commercial design but it is possible that the number was added later.
The loco is well worth restoring and fortunately it seems pretty well complete apart from the safety valve cover.. Judging by the condition of the grate it has done a fair bit of running in the past.
Note that it will probably be to the older 1/2" to the foot scale rather than the more modern 17/32" to the foot.
John
Edited By John Baguley on 20/12/2016 15:56:16