Nutshell-
"RS" VIN GTX- 440 standard, 440+6 and Hemi optional, factory sway bars
"RP" VIN Sport Satellite- upscale interior- 318 standard, 383-2and 383-4 optional, sway bars optional
"RH" VIN Satellite- 318 standard, 6 cyl, 383-2 and 383-4 optional, sway bars optional
"RM" VIN Roadrunner- 383-4 standard, 440+6 and Hemi optional, factory sway bars
...and "RL" VIN Belvedere- base model six cyl std, most everything optional including carpet
"WH" VIN Coronet- Dodge equivalent of Satellite