I am curious what your cars will hold when full. The factory 1966 shop manual that I have says my car holds 20 US gallons. I just replaced the sending unit and drained the tank empty using the drain plug. I put 3 gallons in after replacing the unit then drove 16 miles to get the good fuel. I could only squeeze 15.9 gallons in the tank. Now my 390 likes fuel and I don't cut it any slack so I know there couldn't have been more than 2 gallons in my car which makes a total of about 18 gallons. Tell me what yours will hold.