Keep factory speakers or replace with these?

You would have to modify the speakerbox under the rear shelf package tray. Plus you would get no high frequencies sent to them. I am assuming that you have the MACH460 stereo. Ford went to an 8 speaker design with the 460 stereo. It consists of 4 1.5" "tweeters" running off the Deck with only high frequencies. Then there is 2 amps mounted under the package tray on the speaker box. Each amp is Mono running the front and rear 5x8's respectively. For a stock stereo it sounds pretty damn good. I installed the mach460 stereo (6-disc indash version) in my 93. About to upgrade to Mach 1000 specs. Google that one....

I would call the mach setup mid-grade, so if you are just trying to replace it with mid grade equipment, it's not worth the effort.