The grass isn't always greener on the other side you know. :laughing: If you like one over the other, pick that one. If you want to go by value alone, the '70 will always be easier to sell & probably hold more value in the end. The numbers matching car is desirable to certain people, but in all honesty, not to me. My '71 was a 318 car that now has a 400 inside. I like the car for what it is, & it wouldn't matter to me if it was still a 318 car or not. A big block car will get more & I'd be willing to pay more to have more, but it all depends on the rest of the car.
The amount of rust or the wear on the vehicle, the color combination, the option list are all factors. In the last few years it seems that 4 speed cars are really hot items & sell quickly. I wish one of mine were a 4 speed, but oh well. Body work is the most expensive, & probably the hardest to truly estimate in terms of cost, damage & time. If you think the '70 needs almost nothing body wise, then that may be cheaper for you in the end. I'm guessing that both cars in your garage is not an option? That's my problem, I can't decide what I want.