My first hunch would be cam chain tension, although that sound would be more of a chattering, clunky as the cams rotate.
If your running big ass cams, possibly a cam lobe is tapping a cam cover, or you could be tapping the brass? oil line that goes between the intake and exhaust above cyl 1. I have seen those tap the top of cams even with .395 intake cams.
Also consider if all the bearing set rings have been correctly placed, if the set rings were not correctly placed the cams or gear shafts could slide far enough to make a lot of noise.
Consider removing the plugs, put it in neutral, and slowly rotating the crank to determine if there is any binding within the rotation.
Next, with the plugs removed, and the bike jacked up on a rear stand, consider rotating the engine while in various gears to see if it's in the back half of the engine.
Good luck !!
Dave