Won't start

Well before I get myself into trouble, Exactly where did you measure the 6 inches of vacuum? and if it wasn't directly measuring manifold vacuum then I would ask; "what is the manifold vacuum.

But I think you let the cat out of the bag when you said, that it has pretty good pick-up already. So then my answer would be NO. 10* idle-timing is plenty.
So then, since you have a light, check the timing without the Vcan, at 3000 rpm, and again at 3600. It should be between 30 and 36 degrees. You will need a dial-back lite to see this. Or a timing tape. Or search "hillbilly timing tape".