In 1972 and 1973 you could order the base Challenger with a 340 engine The 340 engine option for the base model also included the heavy-duty Rallye suspension package, performance hood with scoops, and F70x14 whitewall tires.
On JS23 Rallye (1972) and A57 Rallye Package (1973) cars, you had a choice of the 318 standard or the 340 optional. On the Rallye cars regardless of engine, you got the already mentioned heavy-duty supension, performance hood, and F70's. The Rallye cars also had the Rallye instrument Cluster included (although that was an option on the base V8 cars).
The one thing that is unique to the Rallye cars is the bodyside louvers and tape stripes on the front quarter and door.