With dual carbs the two cylinders are basically acting independently from a tuning point of view. With a single carb they are sharing the inlet tract and it must be that there is an advantage to slightly changing the valve timing. If you look at the key slot in relation to the dots and lines you will see that it is a small difference between the two setups.
Did you confirm that the camshaft keys are actually in the slot opposite the dot? Did the engine actually run as set up?
I'll see where the keys are once I get the nuts off the ends of the camshafts. I hope they are installed right, but wouldn't be shocked they are keyed wrong. As for the engine, I honestly don't know if it ran the way it is. Given the heavy coating of old oil caked on the outside of the cylinders and cases, I'd say it ran, but not very well. My dad acquired it in 1990, and I know he's never seen it run.
I suspect that the difference in cam timing between the single and twin carb models was primarily due to a change of exhaust camshaft:
E10043 Inlet camshaft
E10047 Exhaust camshaft TIOOT, TIOOR
E10046 Exhaust camshaft TIOOS, TIOOC, T90
You will only know if the camshaft was changed with the head by detailed measurements of lift, or by removing it to see numbers cast/stamped on it.
My guess is the cam wasn't changed, so the builder left the timing as original.
I'd suggest running as is, I'm sure it would run fine on that setting with either ex camshaft.
If you're curious enough, it is easy to reset the timing gears to the daytona setting just to see what difference it makes. You will have to retime the ignition if you do this, no big shakes.
Thanks for the info, Koan! I'll probably leave the valve timing as it is, assuming the keys are installed right, as Gordo mentioned.