cardumb, Ford only needed 1 speaker per door for a stock system
I persionally think Infinity speakers sound like crap, they "brighten" the sound and do not give you a good representationof what the music should sound like, but hey thats just me they seem to be the most popular speaker at the car audio places these days.
I installed some Diamond audio 5x7's in my front doors to replace smoe cheapo Audiobahns that were in there, wow what a difference!
stock speakers will not handle the power your amp is making, they will hardly handle the power that the stock system gives them, plus yours are OLD, age kills most speakers...
I plan to add Diamond audio 6" components up front and in the rear doors in addition to my 4ea 5x7's, taking the entire system down to 2 ohms with 3ea 10" woofers....
cutting a hole in the door panel and/or making some simple wood spacers/adapters to fit them is not a big issue and should be considered a normal part of this install IMO
Even high end coaxials or components do not cost a ton more then $30 to make, but you have to pay for the name on them to get better sound. Even a cheapo speaker can be made to sound decent given the proper RMS from the amp and a good clean signal to start with, but it seems higher dollar speakers like Boston, Eclipse, etc will outlast and handle more power.
I am super impressed with the Diamond audio line if you couldn't tell....
With audio you are only as good as your weakest link, a cheap head unit, cheap RCA cables, light duty speakers....etc can kill an otherwise good system....