Classic/Antique Car Repair: new speakers match, buick reatta, ohm resistors

Question
I have a 91 Buick Reatta.  I want to install new speakers in it.  The back speakers are 10 ohm each.  My new speakers are 4 ohm each.  How can I use these lower resistance speakers?  I've heard they would be OK one place and another said use an "impedance matching" resistor.  I don't even know what one of these resistor looks like.  Should I get a certain resistance?  How do I install it? Series or Parallel?

I'd appreciate any help you can render.
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Answer
Most sound systems are not very fussy about the impedance of the speaker, so as a first thing to do, try just substituting the new speaker to see how it sounds.  You may find some additional distortion at very high volume, but I doubt you will even notice it.

If you want to avoid that, go to Radio Shack or some other electronics place and buy 2, 5 ohm resistors of at least 10 watts rating and connect one of them in series with one lead of each speaker wire - that will match the impedance very closely, but it will reduce the volume available from that speaker at max volume, again, I doubt you will even notice it.  If you are in the habit of blasting the stereo, the resistors will get hot, so mount them where they won't hurt anything.

Dick