Mine has Comfortron, and I noticed there are 3 vacuum tanks, the rectangular headlight tank by the front, and 2 under the drivers fender. There's a small round plastic one which is teed into a large metal tank, both under the fender. What are those 2 used for?

 

Guessing your car has power door locks. The coffee can shaped tank has a check valve at the top of it and is primarily for the power lock system although the two tanks do work together when both are installed. The smaller plastic tank above it is for the A/C (whether the a car has standard A/C or comfortron, it will use the small tank) and the power trunk release (if equipped). Cars without power locks, will still have the small plastic tank if the car has A/C or a power trunk release.

 

Mine doesn't have power door locks, but it does have a power trunk release

 

That is interesting. My car has both tanks, but also has comfortron, power locks, and a power trunk. My 68 service manual shows the metal tank for locks and 2 plastic tanks for A/C and trunk (1 for trunk with no A/C. 66 might be different. Either way, they are there for the trunk and A/C if you have 2.

 

What does it do with the AC? I guess it's Comfortron related

 

The ball is technically a vacuum accumulator. Idea is stored vacuum will furnish a constant and steady vacuum source to operate vacuum motors. Without it, vacuum operated accessories would fluctuate with changes in engine vacuum.

It's why Olds and others tapped vacuum off the fuel pump diaphram to operate wipers, AC controls and other equipment that needed steady vacuum to work correctly. The vacuum created by the fuel pump didn't fluctuate.