Something fan cooled that you don't have to wrench on. Older Yamahas, Bravo, Enticer, Exciter fanners or the orig Phazers.
That Indy 400 is going to be a tank in powder. Are they good enough to try riding in powder yet?
My 8y/o is starting out on a '80 Trail Cat 440 I picked up. It's really pretty light and I'm certain it will not work AT ALL in powder especially with the cleated track and "cat claws" on it, but good lightweight learner sled.