I dont reall yknow that much about Mach 460. I would never buy a car with it tho. to much of a hassle.
If I were you I would just get you a new head unit and a set of four speakers for the front and year and wire them up your self.
Or if you want get a amp to wire up to the speakers.
No way would I put a head unit on the old mach 460 speakers. I would just re wire it all. Its not as hard as it sounds.
If you were going to rewire it I would go ahead and get you a 4 channel amp since your going to be rewiring it.
But if I were you I would not put a Head unit on stock 460 speakers...... here is why i think you shouldnt
1) the speakers are hooked up to seperate amps
2) if you get a new headunit the headunit is going to be putting out more power than your stock one and is going to run a risk of frying your amps. My friend has a mach 460 in his v6 mustang
and he hooked up a headunit to his amps and his headunit would cut off and distort because it was getting extremely hot.
I went to crutchfield.com and entered your set up and it gave me the full list of cd players for sale. I didnt see them saying anything about by passing the amps so I dunno.
Those are just my thoughts and experiences with the 460