A 71 Satellite and Road Runner were more similar than the 72 models. The 71's had the same grille, the RR hoods were different. RR had a rally dash but so did Sebring Plus Satellite models. Most Satellite's had the standard dash. The RR had different emblems on it and less chrome trim, the Satellite's had more trim, especially the Sebring Plus. There were some differences in the interior but I am not sure of all of them, slap stick floor shift came in both models as well as bucket seats.
The 72 models had a different grille for the Road Runner, it was a 1-year only grille and is very spendy and rare. Everything else has the differences I listed for the 71. The 72 also had a different rear bumper than the 71, the front bumper was the same. The fenders also had different side marker lights between 71 & 72, but there were no difference between Satellite and RR fenders.
If you wanted to make a Satellite look like a RR, I would go with the hood swap, install a rally dash, stripes and wheels, and you will be looking sharp! Also a 340, 400, or 440 would be sweet!
I like these cars too, I still have my very first car, a 1974 Satellite Sebring Plus. I installed the RR hood for looks cause they look sweet, everything else is all Satellite, including the Sebring trim and rally dash.