You sent me rushing to my bookshelf to look ay my copy of the book, but the same thing - no dimensions. I expect you could probably build it any way by drawing fair curves on the plywood as you set the boat out and double checking everything as you went along so that all the components match up. I expect the information will be available somewhere on the internet.
I once built a 'Skimmer' which is the next boat in the book. It was easy to build and a great dinghy, in fact it is an ideal replacement for an inflatable dinghy. A bit bigger than the 'Tortoise' but so practical and a good load carrier.