If you look at the cars from 70-71 and 72-74, the only really noticeable difference is the tail-lights.
yeah, grills changes...marker lights change.
But IMHO those things are subjective,...which do you like better (I prefer the round tailights on my 72 fish)
And of course, engine choices change...But that last one only matters if you want a "pure" car -- ie all original and are willing to pay extra for the "collectability" of the 70-71 with a big block or hemi.
You can take a 72-74 ebody 6 cylinder car and put whatever you want into it.....or take a stock 318 and massage it into something more, or swap in a big block. And have extra money left over because the 72-74s arent getting the "coolectable" prices yet.
For those of us who really that they are essentially all the same cars (or at least CAN be), its a bargain.