Most V8's from 70's and 80's are roughly 4 gallons. 2 gallons water + 2 gallons coolant.
To refill a completely empty system... Add 2 gallons coolant first and then 1 gallon water.
Start the engine with the cap off. When the thermostat opens for first time it will "burp", might even overflow some through the cap.
After it "burps" you should see coolant level drop. When this happens fill radiator to about 1 inch below the cap.
Keep engine running for 5 to 10 minutes. This ensures you don't have steam block in the engine block's water jacket.
Shut engine off and wait about 3 to 5 minutes. Add water until it is up to the level of the cap opening.
Close the cap to first click. This pressurizes to 4 psi.
With engine still hot and cap on, start engine and shut off. Engine should crank normally. If it doesn't, I.E.: the starter drags you have cooling problem, engine or starter has heat soaked.
Wait about hour with engine off ... Check for leaks, over flow, and carefully remove the cap. Add water as needed.
At this point close cap all the way and run the engine to temp or let sit over night and check level in morning along with checking for leaks. Add water to level of cap and fill line of the over flow tank.
Drive the car, when done for the day let sit over night and in morning check level and level in overflow tank.
As long as the engine's coolant is good. Coolant level should be to cap and proper level in over flow tank.
If there is excess in the tank you can suction it out if it's significant, or leave it alone if just a minor amount of excess. If coolant level is low, just add as needed and recheck. Do this for first few days and check level just to make sure no leaks or other issues.
Once everything is good, the engine will be at the proper level with no air pockets in the block. Engine will adjust its self to the proper level.
If you start a cold engine, only running for a few minutes and you get a burp from removing cap ... You have gasket leak and compression gasses are pressurizing coolant.
