I have Infinity Reference Series speakers in my 89. All four are 4" though. Mine lined up fine, although I was told the rears were 5" or 6.5" (I dont remember which they told me now).
Bought a set of 4" and a set of the larger ones. The rears didn't end up fitting so I bought another set of 4" and damm.. I was amazed at the sound of these things!
Everything is so crisp and precise, my only complaint was that there was absolutely 0 bass, no matter how I changed the EQ, bass levels, etc.
Problem solved though, because I got a pair of Infinity Reference Series 10" subs for free. So, made a box for a single 10' that would fit under my targa, hooked it up to an 1800watt amp, and there's my bass!
A little overkill on the amp, but hell, that thing blows out damn near anybodies 2 12"s. And it's not obnoxious at normal volumes.
For $100, I have no complaints about my 5 speaker Infinity system.