There's actually quite a few differences if you closely compare those two underhood pictures. Notice how the black one has that completely different buldge running close to the front edge of the hood that the orange one doesn't have.
There might be a point there with the '71s having the Dodge in the grill. My 70 has dodge on the hood and R/T in the grill whereas my 71 has the R/T (sticker) on the hood and dodge in the grill.
Yeah, you need to show the left and right sides of the hood, it's that main brace closest to the fenders that I was talking about but I think the 70 assesment is probably right. There may have been a certain date (May?) in 70 after which the 70 hoods started showing up with crumple zones too. The crumples are roughly close to the area the hood pins would be too.
It's also not too hard to see the numbers on the hood too if that helps any. I recall a posting pointing out differences and including the numbers.