What brand is it for starters? Go for Mobil, Castrol, Valvoline something like that.
If you dont have the owners manual to look up the correct weight (like 10w40),
search this site or Ford Modifications Website - www.fordmods.com
Ideally get a semi-synthetic type oil. And if you're changing the oil (you should, mixing different types isnt good) use a bottle of Oil Flush before you drain it and change the filter.
NO! Dont fill it to the top! You'll wreck the motor. It'll be something like 5.5Lt or more. It should be up to the top of the COLD dipstick mark. Check again after you drive it for a bit (like an hour).
If you cant get the info elsewhere, ring a Ford dealership. Or ask at the auto parts store where you buy the oil, filter and oil flush.