it's hard to tell without seeing the pan, but over the years Ford has made no less than 7 different pans for the 302 and 351-W engines.....the one used on the early passenger cars,later passenger cars,regular trucks and 4x4 trucks and that's just 4 of them...some came with a single sump, some with a double sump......4x4 pans usually were deeper by a few inches and usually held at least one more quart,so without seeing the pan,it's hard to tell......
But draining and starting with 5 quarts would be a safe way to do it.......or once you drain the old
oil,fill a gallon jug with the old
oil and then pour the rest into another and see how many quarts came out..............chances are it is a "standard" passenger car pan that holds 5 quarts.......
David