yep, me too, so I tried to do some research, type mass air conversion for an 86 mustang, there is such a thing, however I clicked into several links, and none actually explained what it is supposed to do, it is however quite involved (new wiring harness, different parts, and it is not something that would be easy to return back to stock easily, I noticed than a number of applications had bigger cams or built up motors, this is not something that would be done by a middle aged person who drives the mustang on weekends.
This appears to be related to high performance, and possibly a way to introduce more air on a high performance motor. (or one way) personally, anything related to faster, is usually something a younger individual would do, that said, a vehicle may be modified, and may have had some hard use in a racing application, this is not a car I would be interested in as a daily driver , or something that had a adult owner who used it as a normal grocery getter. My advice, be careful, and I suggest you get more information from a mechanic, if you plan to persue this, personally, I would pass on this. I look for cars owned by older adults, who take care of the car, not stick go fast goodies, drive the pee out of it, then sell it to someone else. best of luck. get a complete mechanical inspection before buying ok?