You certainly have good taste in boats, she is a beauty.
Dan is certainly right that you are not going to go tens knots in either flatfish or pilgrim but you might have much more comfortable sailing in rough conditions. I doubt either boat is terribly slow, the Flatfish looks to have plenty of sail area, I could not find sail area on the Pilgrim, and I could not tell if Pilgrim is gaff rigged or Marconi either.
When the word Auxilary is used to describe a sailboat in the first half of the 20th century it means with an engine. I have no idea why its called a North Shore given that it is supposed to have been designed in California.
I completely disbelieve the statement that the 5 hp motor will drive the boat at 9 knts under power alone.
I second rbgarr's reccomendation that you get full plans for a similar boat because I am sure they are out there. The type is not that unusual, its a popular length and there ought to be plenty of plans out there. A quick look at the Atkin site shows a similar boat called Princess Betty though I think the Flatfish is a better boat.
Finally if your going to build it yourself, and your not a serial builder you ought to build the boat of your dreams, not the boat that is second from your dreams.
Yachting, the only sport where you get to be a mechanic, electrician, plumber and carpenter