2000 was the last year of the single DIN head unit, they switched to a double DIN dash in the Mustangs in 2001. I had a factory 2000 setup for a while and pulled it in favor of an aftermarket head unit. There isn't a good factory head unit for these cars IMO. Just get yourself a decent Alpine or Kenwood. You can have bluetooth audio and all kinds of great stuff. Just a heads up, you cars are old enough that the factory speakers probably need to be replaced too.