I bought my copy of Longridge's Cutty Sark book about 35 years ago. It's a "two-volumes-in-one" edition, published by Sweetman Reprints. There's a set of plans, by Harold Underhill, folded up in a pocket inside the back cover.
The plans are good (Underhill was one of the best in the business), but nowhere near as detailed as the George Campbell set. One reason for that is that Underhill was working in (I think) the 1930s, when the ship was still in service as a training vessel. When she was restored, moved to her drydock at Greenwich, and put on public view, in the 1950s, a good deal of research was done to establish her "as built" configuration, and quite a few changes were made to her. (It was at that time also that Mr. Campbell, who was the naval architect in charge of the restoration, drew his plans of her - the ones that are sold by the ship's gift shop.) I don't remember what all the changes were; I do know that they included some alterations of the trail boards and headrails.
The Longridge book deserves every bit of its status as a classic tome of ship modeling. Just how much use it will be for the modern modeler is a little hard to say. In terms of information about the hull and deck furniture, I'm not at all sure Longridge has any more to offer than the Campbell general arrangement drawing. When it comes to the rigging, the biggest advantage provided by the book may be Longridge's verbal descriptions of how the lines lead. The Campbell "Rigging Plan" and "Sail Plan" are superb, but so much information is crammed into them that it may be a little difficult to sort out just how some of the rigging works.
Two other publications about the ship come to mind. The Log of the Cutty Sark, by Basil Lubbock, is the best (and longest) history of the ship herself. And when the big 1950s/1960s restoration was completed, the chairman of the committee in charge of it, Frank G.G. Carr, delivered a paper about it to the Royal Institution of Naval Architects. The paper was published in the July, 1966 Quarterly Transactions of that organization, which later published it as a stand-alone booklet. The ship's gift shop used to sell copies; I picked one up the first time I visited her, in 1978, and lost it sometime thereafter. A year or so I found another copy on the web; I don't remember how much it cost, but it wasn't unreasonable and I bought it. The title is "The Restoration of the Cutty Sark." It contains lots of fascinating information - much of which I haven't seen elsewhere - about just what was done to her before she went on public exhibition - and why. It also contains some photos (all black-and-white) that I haven't seen elsewhere. Highly recommended - if you can find it.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.