I'm confused about distributor advance specs. Also, dual point tech.
I can't really simulate load
Yes you can;
Disconnect the VA from the carb, then Tee a vacuum gauge on the VA, and a long hose that reaches out to the radiator. With your timing light installed, engine idling; just suck on the VA until the timing changes. Then suck harder and read the timing again; and repeat until more sucking produces no more timing changes.
I like to suck the gauge up about two inches at a time.
Then I plot the vacuum and the timing change, on a graph. Now I know exactly how much my timing will change, at any rpm, with varying load.
If you have a mity-vac, use it, cuz when you get to 15>18 inches, sucking on that hose gets to be a chore.
As to adding washers,
that increases the spring-pressure, which then requires more vacuum to achieve an increase in timing. So then, at 10 inches, the timing will be LESS than listed.