Agreed.
Most any speaker can be made to fit, it all depends on how much $$$, time & ability you have to invest in modifications to your door panels.
As Dave stated, the factory OEM size is 6" x 8" so any of the readily available 5" x 7" or 6" x 8" speakers should drop right in, depending on mounting depth.
According to the Crutchfield fitment chart, the mounting depth for the front speakers is 2-3/4" & rear is 2-1/2"
There are several models & manufacturers to choose from in addition to Pioneer, so just shop around & choose those that most appeal to you & your musical tastes.
1999 SVT Contour, #2140 of 2760, Tropic Green - Medium Prairie Tan
Koni Sport struts; TSW Blade wheels; Nakamichi, a/d/s/, Boston Acoustics, Infinity I.C.E.
1989 Saleen Mustang, #89-0408, too many mods to list here
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