you can lighten it more if you remove those wheels you used. get some factory yamaha ones that came on the sleds new. the bearings are not replaceable but they are super light. just lift the seal and grease the bearings. also the rear billets are heavy, they also load up with ice in some conditions. Use the factory rear center wheels with molded bearings, even the ones with removable bearings are light. drill some holes in them to make them look a little better and you have one of the lightest wheels you can get without going carbon.
also, up front, used to be able to get aluminum shafts for the a frames from barkbuster. they had issues with wear and stopped making them. These would still be light if you sleaved the areas that wear with stainless. I would guess a 2-3 lb savings there.