This might not necessarily be a stupid question.
On the 1964 Thunderbird, the oil filler sits right on top of the manifold, behind the
radiator surge tank. Lift off the filler cap, bada bing. BUT -- does this car have the original engine with the original intake? If the car has an
Edelbrock intake, guess what? No filler. I believe you could buy them long ago, but not anymore. If you have an aftermarket intake, those THUNDERBIRD valve covers must come off and be replaced with 65-66 types or some chrome aftermarket, with a filler cap on the cover. If you don't have either, you might have to use a nice funnel and go in through the dipstick. This is stupid, but I've seen it before.
By the way, my avatar seems to look a lot like Mr. 64Zcode, but I don't think it's the same car (unless he snuck over to my house and took a picture of mine). Mine looks like a cornucopia with a trunkload of old car radios.