The first year for the FXRT was actually ´83 with a shovelhead motor and an enclosed chain final drive. That year had dual disk brakes in front also. In ´84 the FXRT was one of the models to receive the first year EVO motor, a big improvement, but for some reason they went to a single disk brake in the front. In ´85 the FXRT was upgraded to belt drive and dual disk brakes. From then until the model was discontinued in (I think) ´92, it received the same upgrades as the rest of the FXR line as far as I know.
One other set of changes, in ´83 and early ´84 the FXRT had a dry clutch. The wet clutch upgrade was introduced during the ´84 model year. In manuals, parts catalogs, etc you will see a reference to Early ´84 and Late ´84.