You can easily spot an FXR by the frame tubes that make a triangle under the seat. The FXR was the plain jane no chrome model.
FXRS in the Shovel years had a little more chrome. In the first couple of Evo years it was the Low Glide and then became the Low Rider with tank-mounted speedo and tach.
FXRS-Sp was the sport model with handlebar-mounted gauges and taller suspension. FXRS-Conv same as Sport but convertible with removable bags and windshield
FXRT had a frame-mounted fairing and hard bags, taller suspension.
FXLR was a custom with lower suspension, same as FXR, FXRS and different speedo, wheels and tank, the only one not to have "R" as the third letter.
FXRP Police model with sprung seat.
Those were the main models, but there were some others over the years; FXRDG Disc Glide, FXRD touring deluxe, FXRC custom...