Hey John... The original Tricubs that I have seen in person and in early ad photos all have the tire chevrons pointing toward rear as viewed from top. The general consensus is that this configuration is best for more fluid-like surfaces... sand, snow, wet mud, water (AATVs). The more traditional tractor config (chevron pointing forward) is better for firmer surfaces like turf, dirt, thick mud, etc. The ski on mine is SPD factory ski kit. It looks very close to sled skis from that era, but I have not yet seen exact match on any production sled. I believe that SPD bought this ski as shelf item and added the axle bracket to create their kit. They offered this kit on Tricarts and Tricubs... only added spacers for Tricarts to make up for longer axle length.
Regarding the seat, there are at least 2 different Tricub versions. One, as in some of my earlier Tricub photos, with unpleated, smooth cover sewn directly to a plastic shell that snaps to the body. The 2nd type is a pleated seat cover, as shown on some of my later photos, that snaps directly to the body with no shell. I had one of these made at an upholstery shop from photos and it looks good and works well. I've never seen a loose Tricub seat for sale and even most Tricubs I've seen for sale have no seat at all.
Good luck with your project... let's see some photos
Tricart/Tricub ski kit