This looks to be right:
http://www.installdr.com/Harnesses/GM-Wiring.pdf
The connector is different, but the color codes seems right. The only disagreement between the 2 shown in the link above is in the Right Front color polarity (lt green/dark green)
Depending on your original radio, you may not have the provisions for a "constant on" wire (orange).
Use a voltmeter or test light to determine your power connections.
As for speaker polarity (assuming you are reusing the ones already installed), use a 9V battery and connect to speaker. If paper pushes out, the polarity is correct. If paper goes in, then you have it backwards. Do this BEFORE wiring the radio.