I would use a 13 mm wrench. If you don't have one you should get one ! This and 10mm are the two most common metric sizes in bolts etc. -For now you can also use a 17/32 wrench or a crescent wrench.
You use a 16 mm or 5/8 wrench.
An 18 mm wrench is ideal, but if you don't have one of them, you probably won't have a 23/32 either.
The oil drain plug uses a 13 mm wrench.
You need a 15 mm wrench.
13 mm13 mm
It's a 13 mm wrench
It is not Allen . It is a 14 mm open wrench
14 mm
7 mm Allen wrench
15 mm
Generally on that age of Fords it is a 13 mm wrench.
13 mm