Speaker impedance

I have an old Chevy Cavalier convertible with the factory AM/FM
cassette player in it. The rear 6X9 speakers are missing.
I have several old speakers lying around, which would be good enough
for what I use the car for -- but the impedance listed on them varies
between 4 ohm and 10.
Meanwhile, the radio doesn't have any marking on it regarding how many
ohm speakers it requires.
Or does it even matter? What would be the possible consequences of
using speakers of the wrong impedance? This is just a low-power unit,
probably 3 watts or so. TIA

 

Using speakers with too low an impedance could overheat driver areas in
the radio. Usually, though, an impedance mismatch only hurts the power
the unit will deliver. Most radios will drive anything in the 4-8 ohm
range fine. 8 ohm replacments are a good choice, though 4 ohm will
likely work if you don't crank the volume up full.

 

If they are good speakers, they will work just fine.