I have been told that the '69 gas tank will drop right into a '65-'68. I haven't verified this, but could easily measure my '69 and '66 tanks tommorrow, if need be. The '69 and later tanks get there extra capacity mostly from being "taller". The '69 tank is about 2 inches taller than a '66 (which I believe is the same as the '67). If originality is of any concern, this swap would not fair well, as it would be very noticeable mod.
BTW, the '69 tank is 20 gallons. I believe the 22 gallon tank started in '70.
If you always do what you've always done,
You'll always get what you've always got
You can put the '70 22 gallon tank into your car. Use the 70 sending unit as well. You might need to make a conversion connector to connect the sending units 3/8" hose to your fuel lines 5/16" hose. The biggest problem you'll face is the fitting of the filler neck. You will need to cut off about a 1 1/2" but the angle will be off. By using a longer filler hose you can tighten the clamps to get a good, secure seal. Or better yet take the filler neck to a muffler shop and have it tweaked before you trim it. I have done this on my '66 without any problems and I can go longer between fill-ups!
National Parts Depot
1965 Conv:Street driven concours
1966 Coupe: Daily driver and toy
Yes, the 1970 Mustangs had the largest fuel tank. And these 22 gallon tanks will drop right into the hole in earlier Mustangs. As mentioned, some filler neck mods are necessary, but well worth it.
A friend of mine installed a 1970 22 gallon tank into his 1968 convertible. It was an easy install. I noticed the difference when we drove to Steamboat Springs with a 1965 Mustang that had the factory tank. She had to stop for gas when we still had plenty.