I can tell you after working on cars for 20+ years of all sorts from 59 Chevy Impalas to Mustangs and 931 Porsche I was intimidated to work on the Norton when it was accquired! Heck, I can drive Bradley Fighting Vehicles, M1 Abrams and just about all the wheeled vehicle inventory in the United State Army and the Norton still had me nervous!!
I agree with all that state you need to find a complete or 90% complete bike to start with. All the little doodads and widgets that go into making a Norton or any bike to go are numerous and can turn out to be quite costly. Just buying turn signal pods and stems will run you 20-30 bucks unless you want original Lucas, then that can get close to $100 for a decent set when found. I have a 74 Roadster that was complete but once I finished with mainly basics (Tires,hoses, brakes, battery, petcocks etc) and upgraded to Power Arc electronic Ignition and oil tank modification from CNW, I was in the bike for $3000! If you just start with an engine and tranny you might as well call Matt Rambow at CNW and have him do a custom job for you, would probably be same price wise!!!
I live in Mississippi and have seen very few Nortons but there is one on craigslist in Alabama going for around $6000 if I remember right and it looks good from pics but you cannot trust those! $1500 for a drivetrain seems a little over the top and what if it is bits and pieces inside? Then you are looking at a decent wad of cash to get the parts and have the machining done!
Find you a good running or barn find Norton and go from there. It is better to have as complete a bike in front of you starting off new on these babies. Flea Bay usually has a couple on there alsong with the IONA site, even here. Good luck and welcome to the board.