318 Idle Questions

68 no upgrades would have mechanical points. Loosening screws inside may have changed the point gap.
Some of the original tuning specs were quite strange ( like 0 +/- 10 ). Anyway.. none of those really apply with todays lower octane fuels.
The vacuum advance should have been attached at venturi or timed port so shouldn't make a huge difference whether it hooked up or not a very low idle. That is unless the advance plate is simply worn out , in which case the advance could close the point gap completely when the vacuum hose is disconnected.
I suspect everything about an original 68 points distributer is worn out.