06 600 track change
You can use the WPS 44-1513 extensions. They are for a 10" gain in track length, but will work in your application because the new drivers you must use are slightly larger in diameter, 2.86 pitch x 8 teeth versus 2.52 pitch x 9 teeth. There are a few other problems to deal with however. You will need a tunnel extension to run the 155 but not the 151. The 06 IQ chassis is 25# heavier than the 07 and newer IQ raw chassis. While the 07-11 600 RMKs turn the 155 just fine, a stock 06 will struggle, even with gearing changes. The Polaris Series 4 151" x 2" track or the Camoplast Challenger 151" x 2" will go right on and give you more track speed and less hifax issues than the 155.