I don't know enough about the history of the bike or the rider. Here's what you need to know. When dual plugging was originally set up was the ignition tailored for this. Dual plugging involves customizing the ignition curve sometimes no more that just making sure the F dot is not in the window at full advance. Ignition timing needs to be retarded for dual plugging because two plugs burn the gas faster.
So when you put a timing light on the timing window and time the bike, what sort of picture do you get in the window, at idle? At 3000 rpm?
There should be a custom mark of some sort, usually a paint dot, on the flywheel. May also be a dot hammered into edge of flywheel with a hammer and chisel. This mark should appear before the OEM dot when turning the engine in the direction of normal rotation.
Again the point is a dual plugged engine needs custom timing and if you didn't build this thing then the person who sold it to you should have told you something about it.