I'll put my vote in too for replacing the rearfactory speakers with 4x10. No need to modify anything. Pioneer or eclipse make great 4x10 speakers for rear fill.

The important speakers are the front ones. My old, old cavalier had 3-1/2" dash speakers. I tried both the Kicker 2 way and the boston 2 way. I couldn't get enough sound up front so i added components in the doors as well. That worked great. I had a 2 ch amp for each side, but you could do that with a 4 ch for the front as well.
You're best off to get an amp that has variable hpf for each.

In my last car i went with 2, then 3 way for the dash and dedicated midbass for the doors.

good luck.

__________________
Alpine CDA-9887, TUA-T500HD, CHA-S634, CHA-1204 & KCA-410C
Pioneer TS-A6981, 6 x GM-5100T
Kicker 2 x CVR15,
MBQ RCE-216
PG MX2
Soundgate LanStar1
PAC SWI-ALP

Wow, thanks for all of the responses!

I'm going to take your advice and go with the 4x10's in the back (easy and cheaper!).

When I get some bucks built up, Ill install some kickpanel speakers, that way I won't need to wire through the door. The subs in the back will be easy. I'll just make a custom enclosure (farmboy here, pretty handy with tools) and stick them in the trunk.

Don't want to spend a fortune! Next year I'm planning on a 350 with headers, so I need to budget my money.

Thanks again guys, I'll post pics when I get them.

If your car's in decent shape, then don't cut it up.
Some AP kicks, and tweets in the dask, with a bit of EQ down around 2.5kHz should be pleasing without being annoying, and use the 4x 10 holes to vent the sub's pressure into the cabin.
Your back window is vertical and will give you no gain from a rear speaker.

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Charlie Lamble
Sault Ste Marie ON

I'm sure you think you understood what you heard me say, but I hope you realize that what I said is not what I meant

Ok, so if I were to replace the 3.5's, and stick some kickpanels in, there is no need for rear speakers?

How would I go about building a box to vent my subs through the 4x10's hole. Would I build an enclosure, plant the subs vertical and point them through the 4x10's?

How hard are kickpanel's to install? I will be building my own, instead of throwing my money out on Q-Logic. I'd likely have to pull out my e-brake on the drivers side (which I never use anyway!). Just nervous about figuring out how to run new wire to the kick panels. Hopefully it's not too hard.