buell is correct with the Sporty changing sides in 1975. Modern beltdrive
started on the Sturgis in 1982. The Sturgis also had a primary belt. In 1983 the FXDG and FXSB received belts. 1984 was the tourers and softytails. 1991 started the Sportys turn. All this info is from The Encyclopedia of the HD by Peter Henshaw and Ian Kerr. Very interesting reading.