Building purely to sell depends on a lot of circumstances - that is, how desirable the machine is, how much you pay for it initially and how much you have to spend to get it roadworthy and licensed. In the end, unless you have a barn-find vincent or similar, its unlikely youll make much profit at all (if any) - although if you just happen to enjoy the rebuilding and not riding, its the best option.
I beg that you dont sell it for spares if the engine matches the frame - im one of those people that reckons if the factory made it that way, it stays that way (curse you triton owners! bring back the featherbed singles!)
Riding a bike youve restored is a very rewarding path, and i think if you build it to an easily rideable state (which is certainly not difficult to do) then you will enjoy the bike regardless of how handling/braking/power compares to modern bikes. If it is a 1968 bonnie (which is a T120 not a T140) then it should handle quite well and with the correct twin-leading-shoe front brake will stop well enough. And i think most people here will agree when i say that 650 bonnies are just bucket loads of fun to ride
So after all that my conclusion is you should ride it when youve built it. Put it this way - if the engine and frame are done, youre more than halfway there. if you find you dont like riding it once its built, you can always sell it then and probably not lose money
my 2 cents at any rate
