Coming from someone that made a 70 from a 74, I would say save up for the 70 or 71.
http://www.cuda-challenger.com/cc/index.php?topic=24142.msg236297#msg236297If I had to do it over again, saving up for the 70 is what I'd do. However, the car came out great. Only an extremely trained eye would be able to tell the difference, and parts and labor only added about $5000. (That's w/o the paint job, which was going to happen in any case.) I might have saved a bit of money, but it was a hassle, and probably will be a hassle for quite some time. The NYPD auto crime unit pounced on it thinking I was going to change the VIN, many enthusiasts (such as moparnocar) scoff for obvious reasons, and I'm sure that most people will suspect I did if for nefarious reasons.
I came into the Mopar world via their full size 4WD trucks. Anything goes there as far as mixing and matching and modifying. I put a ‘93 grille on my ’85 Ram. My ’74 Power Wagon has a ’79 grille. I just took mentality with me when I got into the muscle cars. Now I’m a bit more indoctrinated, but it’s too late for my Barracuda.