All of the Turbo-Fox setups I know of use the mass-air conversion if the car was originally speed density.
And as far as the Supra Turbos are concerned, I have no idea. There are just too many Mustang-oriented turbo options out there that are made for the fox to worry about mixing and matching parts.... (in my opinion)
__________________
Uncle Sam
"What the hell is up with all the gauges?
Calling Captain Kirk, your ride awaits... Phasers on stun...."