Bamamav hit it on the head. Ford had TWO types of fills on their 9 inchers, one was on the housing and the other one had it on the pumpkin. If you mismatch them and put a pumpkin with NO filler on a housing with NO filler you have a problem, Bob.
You also need a way to check the gear oil level, and the filler plug is the way this is done, and since you have none, you have no way of knowing how much is in there.
What I would do is drain out all the fluid, then look up how much yours holds, then put that amount into the vent tube fitting. Not a perfect way to do it, but it will work. (my 9 incher holds 2 quarts)
But look on the drivers side of the pumpkin and you might see a square hole in there. It takes a 3/8 rachet and that removes the pipe plug, if you have one. You could just be missing it. Fill it with 90 wt gear oil until it just dribbles out the hole. If you have a limited slip, put in Ford Racing additive to make the clutches work right.
Don