[Artie]

I would take both cars into consideration, 71 production numbers are lower than the 70 making it a more appealing car. However not having the original engine will hurt the resale of the car if you need to sell it down the road. Given the fact both are 4sp cars doesn't help much either, it's no secret they bring more than an auto car. I personally have a 70 blue/blue car. I chose to put a 455 in it. You may know the car, it was on the cover of HPP April 04. I have modified the car to my liking and don't particularly care about resale.
You have to decide what you want out of the car, a stock numbers car or a radical car built for serious fun. Also you had 2 choices for colors, blue or white, which do you like more? I would also look at which car would require less work to restore. You can use alot of parts you bought on either car most likely. The only real differece is 455 high back buckets or 400 low back buckets. Blue or white. Other than that, they are the same. I would keep both but everything does have a price.
I just started restoring a 70 for a guy in FLa, pulling the 400 and the 4sp out and installing a 500+ hp 455 with a 5sp richmond in it, he said it wasn't fast enough and it needed another gear. It's a white car with black interior. I will be upgrading the brakes and suspension as well. Build either car hwo you want, you can always do like this guy is, tuck the drivetrain under wraps for the next guy!