I have an 08 600 rmk 144 that I am looking to sell this spring. It is a very nice sled and I love it for riding in the Upper Peninsula of Michigan. Handles great and is awesome both in deep snow and hitting some jumps/moguls. No modifications to the motor or clutching but I have a MBRP can on it and I have fabricated a bunch of vents myself. I am currently in college so I did not have enough money to do major modifications. This sled looks VERY sharp and would be awesome for your boys. I love the way it handles, and the only reason I am getting rid of it is because I am ready to have more power for trips out west. If you are interested I can send you more pics and give you more info.
I have an 08 600 RMK 144 for sale in Washington state. Mileage is 8XX, I can check exact mileage if you want. I am asking 5200, but am open to offers. My daughter rode it for one season. Great sled, no issues. There is a picture of it on the Polaris swapmeet. My number is in that ad if you want to call.