Don't let the fact that this reply is coming from a guy running a 240 scare you off.
Some engines had what are called "loadomatic" setups. The Autolite 1100 carbs (maybe Holley 1904, 1940 too?) were coupled with a vacuum advance only distributor. Later dizzies have weights and have a mechanical advance that advances based on RPM as well as vacuum.
Anyhow, the early 1100 (maybe some 1101 too) carbs will have a "spark control valve", which sits on the passenger side of the carb, sort of behind and above the ported vacuum line that goes to the dizzy. This valve uses a combination of ported (above the throttle plate) and venturi vacuum to advance the spark. This combined vacuum is weaker than your usual ported vacuum, and it takes a special dizzy that has a more sensitive vacuum unit. In short, the carb and dizzy function together. Swap one or the other out with the wrong components, and you may have trouble getting the correct advance.
Now, I beleive that all dizzies that have dual vacuum hookups were from a later era. After load-o-matic. You block years are after loadomatic, but stuff gets swapped onto block that don't belong there. The second, "outer" vacuum hook was to retard the spark, and it had to do with polution stuff. I think. Anyhow, as you noted, leaving the outer one hooked up to nothing is OK. In any case, you can easily verify whether you have a dizzy with mechanical advance -- take the cap off, and twist on the rotor. If it moves in one direction maybe 20 degrees (1/18 of a turn about) and then springs back when you let go, it has mechanical weights and springs in it.
If it is solid, and has no "spring" to it, and has only whatever play is in the camshaft gears or dizzy shaft (should be pretty minimal) then you have a loadomatic dizzy.
With your weber, you cannot have a loadomatic dizzy. If you do, you'll need to get a new one. The correct later dizzy is often listed as a "thermactor" dizzy. In reality, the thermactor system has NOTHING to do with a loadomatic setup -- but they were phased in the same year the loadomatic was phased out. Or so I understand what I have read. I am not a big 200 afficianado (sp?), but if a duraspark is available for them, and if you have a loadomatic, then now is the time to upgrade all the way to electronic. FYI, pertronix is available for both loadomatic and later dizzies.
Why does a guy running a 240 know this? Cause the 240 had a loadomatic setup for ONE year, 1965. And when I inherited mine, it had a later 1101 Autolite carb without spark advance valve (non loadomatic) , but it still had a vacuum only loadomatic dizzy. When I swapped to the correct dual advance dizzy and upgraded to a Carter YF, viola', much better performance and advance.
Good luck
