I think the inlet hose is 2" on the inside diameter and the 5.0L has larger diameter EVERYTHING on the intake so i don't know if a "cold air intake" will work on your car. The intake for a 2.3L is designed to be very quiet and is VERY restrictive. If you can get some flexible hose you may be able to make an adapter for the 5.0L designed filter assembly to the mass air meter (using hose clamps to seal it). Another modification you can make is to get a throttle body off of a 3.8L thunderbird, it's larger so it flows more air (from what i hear, but i'm not 100% sure it'll work, but i think it will). If you have the intake tract muffler (the big round thing in between the throttle body and mass air meter attached to two hose pieces) with the Ford logo on it you can cut out the inside (it goes down from 2" inside diameter to 1 1/2" because of it) with an exacto knife and you'll pick up some power. If you have the hard round one, you could easily pick up a Ford logo one from a junkyard for real cheap or you could find some pipe or something to put between the hoses. Good luck!
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT