There were lots of subtle changes but the shape of the cars didn't really change from 70-74, as with Challengers.
The 70 and 71 Cuda's are by far the most popular but all Cuda's are collectable and rare, especially the ones with little or no rust.
Cuda's are the high performance version of Barracuda's, sort of like a Bernaletta Camero is the low performance version of the Z-28 Camero, same skin but most everything else has been subtly upgraded for performance.
1971 seems to be the peak Cuda in popularity with the gilled fenders, cheese grator grill, bill board quarter panel graphics, etc. The 1970 model lacked some of these "frills" but in my opinion looked a little meaner with it's no nonsense and clean looks, especially when painted black! The most popular options on either year car (now days anyway) seem to be the 426 Hemi engine, the rear "Go-Wing" spoiler, the Shaker Hood, and 15 x 7 Rallye Wheels. The Bill board decals on 71's seem to be high on the list as well. Want to see a 70 and a 71 comparison? Look at the flashing pic on the left of my posting, the green car is a 1970 Barracuda convertible, the orange one is a loaded 71 Cuda convertible.
Engine choices for both years were the same, Barracuda's had either a 383 2 barrel, a 383 4 barrel, a 318 2 barrel, or a slant 6 (yes, believe it of not even the Barracuda had the slant 6 as an option!)
Cuda's had a base engine of the 383 four barrel or the 340 4 barrel at not additional cost, the 440 4 barrel, the 440 Six Barrel, and the 426 hemi were all extra cost options.
Transmissions were either the 3 speed manual, the pistol Grip 4 speed manual, or the 727 automatic with slap stick shifter.
I'm pretty certain the above info is correct, any critics out there feel free to correct me
