people always rag on speed density, but the truth is mass air only has one advantage, and thats automatically adapting to minor(I stress the minor part here) mods....speed density is fine....if you dont like it you can convert to mass air....personally I will never use a mass air setup, I think the mass air sensor is another useless sensor that contributes to throttle hesitation on EFI cars.(at least from my understanding, the lag between the time the air is measured and actually enters the intake ports, at least naturally aspirated speaking) To me, the best system is a programmable speed density setup....true, you have to re-tune for every mod(for an ideal tune anyway) but you dont have to deal with MAF sensor costing hundreds of dollars you have to upgrade...the throttle hesitation doesnt exist, and its a simpler system and I am all for keeping EFI simple...the OEMs try to complicate it too much)
From my understanding, hardware to re-flash ford ECUs(speed density or mass air) is readily available