I want to say 5-6 Qt, but you should ask your mechanic.
Transmission fluid
transmission with 2 wheel drive is 24 pints transmission with 4 wheel drive is 27 pints
If your changing the transmission filter, it takes five quarts. If the transmission is completely empty, it takes about ten quarts to fill it up.
Type F for a 1971 C6
Yes, Type F is the correct fluid for a 1971 C6.
Type F
A C6 transmission including the torque converter will take 12.5 quarts.
Use type F.
No F is ford type fluid.
C6
Motorcraft MERCON automatic transmission fluid ( for the C6 / 4R70W / E4OD automatic transmissions ) - according to the owners manual
Ford C4 Automatic Transmission refill capacity (approx): * C4 / 302 c.i. = 9 US quarts * C4 / 351 c.i. = 10.25 US quarts * C6 = 12.5 US quarts * FMX = 11.0 US quarts Use Ford "Type F" fluid Source: Haynes Ford V8 Mustang 1964 1/2 thru 1973 Automotive Repair Manual