I agree with Fast Eddie, unless you're just wanting a big challenge. I'm almost finished rebuilding a 1972 750 that was more or less complete when I bought it and it came with some spare parts I could use/sell. Forgetting my time, I'm into this rebuild for over $8000 so far. See:
http://gregmarsh.com/MC/Norton_1972.aspx to get an idea of what it takes to rebuild one.