The "system tank" is the shorter of the two tanks, it has two 13/8 hoses attached to the side. It should be mounted closest to the engine. The upper hose (inlet) comes from the engine outlet, the lower hose (outlet) attaches to the plumbing that feeds the radiator. That's the tank that should be equipped with a 13 psi radiator cap. This tank serves no other purpose other than to be a convenient place to locate the radiator cap.
The taller tank acts as the coolant recovery tank. There are no connections for the larger 13/8 hoses. The overflow hose from the filler neck of the "system tank" connects to the bottom of this recovery tank. The cap for this tank should allow the tank to be vented to atmosphere.
If the cooling system lacks the "head tank revision" as detailed in Chuck's (Rocky's) drawing, then the left hand tank of the radiator should have a petcock screwed into the fitting located in the top of the tank, making it possible for you to vent air from the radiator manually.
Start the engine, keep the recovery tank half full, leave the cap off. Turn the cabin heater on for full heat (this purges air from the heater core). Once the engine reaches operating temp raising the front of the car will help any air in the engine or the plumbing downstream of the engine to flow towards the radiator; then raising the rear of the car will help any air in the radiator outlet flow towards the engine; then raising the front of the car again shall help any remaining air flow towards the radiator. At this point all the air in the system should be in the top of the radiator, opening the petcock in the top of the left hand radiator tank should allow that air to flow out.
Keep the level of the recovery tank about 1/2 full when the engine has cooled to ambient temperature.
P.S. whimsical note from the forum admin. You did an excellent job titling the topic and selecting the forum! 