Hey Aaron,  I don't see any problem for the factory radio in replacing the stock speakers with aftermarkets. I recently changed out the original 4x6's (10 ohm) with a new pair of 4 ohm 2-way speakers, and the overall sound quality is improved. As always, avoid turning the volume up past the point of distortion (clipping).  

Nope; I'm not certain that you can't, but a quick google search turned out these 2 interesting thread:

1) forum where the guy seems to say you have to use 10ohms aftermarket (sorry for a link to another forum...) http://www.digitalcorvettes.com/forums/showthread.php?t=38469

2) this guy sells classic car speakers and has really good info.  Seems like not having hte correct ohms would make the wires run hot... too hot....
http://www.turnswitch.com/speakers.htm

Again, I don't know for sure, but something's telling me you have to find the correct one's.  Even if the sound comes out fine; it doesn't mean you won't burn the wires...

You don't have to buy from him.... but give the second guy a call; looks like he knows what he's talking about!

and btw; you will most likely find out that aftermarket 4x6's don't fit "exactly" in the original 4 holes.  I think I got 2 ok, a 3rd fine and forced the 4th.  If I remember correclty, I had to bend/twist the speaker bracket a bit.

Steph.

     Hey Aaron, I've still got those Delco 4x6 (10-ohm) speakers out of my '78 that you are welcome to have. They are in good shape - I changed them for speakers with tweeters to get more highs for my tin ears. I will be glad to send them to you, just PM me or send an e-mail with your shipping address:

i appreciate the offer, but i'm going to put new ones in. After all, the dash is already all apart.