Apparently this was a one-off, rather narrow for its day, which was designed and built by a couple of scientists. According to the N12 site:
Uncle Stalky is a combined design effort by Jim and I [Chris Aldis] during our student days as respectively applied and theoretical physicists. Jim was at Bath and sailed on Cheddar and I at Southampton sailing at Hamble. Jim had already designed and built N2401, Bunyip. We designed Uncle Stalky specifically for my light weight for inland racing in lightish winds. Jim did an industry placement as part of his degree and worked at the NPL ship test facility at Feltham. Very useful when designing Nationals!
There were a few unique aspects of Stalky for the time. 'He' was only a 6 planker when all other 12s were at least 7 planks and the strake at the bilge turn at the transom was merged with its neighbour to show only 5 planks on the transom. It is very neat and shows Jim's eye for a pretty design.
I raced Stalky intensively in 1970 to 72 with considerable success, I think we came 2nd in the Burton in 70 or 71. I think we also had a grand slam at Salcombe about then as well (my favourite sailing venue).