Wheels swap to all years with no problems. The front axle changed by 1/4" at some point, but i can't remember when that was. The rear axle nut changed as well, but it shouldn't affect anything.
IIRC the rear axle did in fact changed in length when they changed from a 27mm castellated nut to the newer style one. The older axle has a cross drill for one of those below (don't recall the name in english). Wheels just change in looks.
Front axle stayed the same from all that I have seen. Rear axle changed in length as noted (shorter) in the later model bikes. They do not have the cotter pin hole drilled since they did use the self locking nut. The reason for the length change was due to a change in the rear diff housing where they have a casting used by the royal star line for a speedo sensor (looks like a tear drop shaped casting just in front of the shock mount location).