So the factory speakers in my 97 k2500 im pretty sure are 10 ohm speakers.
Measure and find out. "Rated impedance" is generally a bit more than DC resistance, as measured by an ohmmeter. If they measure 9+ ohms, they're probably "10 ohm" speakers
However the set i want to install are 4 ohm. What can i expect?
I asked the same sort of question when I had a speaker fail on my '93 Lumina. I was told that the standard GM radio/cassette unit was compatible with 4-ohm rated speakers. I slapped in a pair of aftermarket 4-ohm speakers and got better sound than the cheap OEM units.
Are they going to be louder or quieter?
Is there going to be distortion?
No way to know. "Louder" or "quieter" is not dependent on the impedance. It's dependent on the sensitivity/efficiency of the speaker. IF (big IF) your electronics are not compatible with the reduced impedance, there could be distortion.
Adding resistors to compensate is a horse-**** method of fixing the problem, because you'll kill the volume. Then you turn the volume up to compensate, which heats the resistors and increases the value. Then you have to turn the volume up even more. Eventually you're running the radio so hard it cooks.