90mustang325hp

hey everyone, i need some help with my mass air flow sensor i bought a 1990 gt mustang from a guy that had it sitting for a while and when i got it there was no mass air flow sensor on it and i just finished the interior and everything on it and getting ready to drive it, i went to my local autoparts store and they told me there are three mass air flow sensors for the car it could use. which one of these do i need? does it matter which one i buy? it is a 1990 mustang gt 5spd... please help!