Audio Systems: 1998 Lincoln Mark VIII, lincoln mark viii, premium sound system

Question
This '98 Mark VIII came with the JBL premium sound system.  
1)Is there a later-model Ford/Lincoln head unit with CD-MP3 and cassette functions that's a drop-in fit?  Also, if necessary, I can do without the  cassette.  

2)Infinity makes the 6820CS, component 5x7/6x8 speakers in 2 Ohm, with separate crossovers included.  I understand that the JBL OEM amp has a crossover.  If the amp has a crossover, do I just replace the speakers and rely on the crossover in the amp; that is, for this appliction, is there no need for the Infinity crossovers?

Thanks,
Guy

Answer
Only Ford CD units from that era would work, and they are going to be very well used by now. Better to upgrade to a new after market unit, using a proper interface from such companies as Schoshe, PIE, Peripheral, or Metra. As for the speakers, avoid anything 2 ohm. Stay with the standard 4 ohm speakers unless you are going to remove the JBL amp completely and install new after market amps designed to run 2 ohm loads. Pioneer makes nice 6*8 speakers, and they fit perfectly. It would be charitable to call the filter in the JBL amp a crossover. It is really just a bass blocker. If your new speakers come with crossovers, use them as well.

Kelly