Blackdogzulu - here's the deal. Yamaha made many different parts for their bikes over the years. My 86 xt 600 was manufactured for North America. Some parts on the bike are different than those in Europe and elsewhere. For instance: Yamaha no longer offers a conversion from off-road to S/L for North America, also Yamaha is no-longer offering dual-sport bikes for North America. Our Gov't has changed the rules and ****ed us over.
Now about the shaft and sprocket - the shaft on my bike is splined half way down the shaft leaving a small space with no splines. the splines continue on at the base of the shaft before it disappears into the case. Therefor the sprocket resides in the middle of the shaft with only the two outside edge making contact with the splines. The retaining clip attaches to the spline gets turned to line up with the holes in the sprocket and bolted down. There is no center bolt and the shaft is not machined for one. The sprocket is in contact with both splined areas. the 'free-play' is so minuscule it cannot be detected by using your hands. Only under torque loads will the 'float' occur. Just as the rear hub/sprocket has rubber torque wedges to absorb some twisting force, the front sprocket does as well. hope this helps you understand the concept. As I stated earlier as soon as the parts arrive I will post pics of the shaft for you to see - before assembly and after.