Tom,
I know of it but its said to be inside the NR boundary and so haven't seen it myself. I had a couple of friends from from my Bodmin & Wenford days whoose day time job was on permanent way with Railtrack as was; nothing to see was their reply, but I'm not convinced of the location being correct. I suspect a looks needed at old GWR route plans; I believe now held by NRM with NR having digitsed everything and passed the originals on, next time I'm in York (a fairly regular occurance) I'll investigate.
Yes, lots on the Mount, what with the one on North's, trucated remains on Merediths (the chimney was a known bat roost) - I think that's the one your refering to, stamps engine etc.