If I do purchase the 71 as a donor. I plan on taking my radiator support, cowl off my 70 and put it on the 71. I did not check the 71 for ac so if it does not have ac (firewall) then I would change that out as well. I think that is the only two places that woulg have the matching nubers. So I would basically make the 71 a 70.
John
What your suggesting here is called rebodying a car, and it is considered a Federal crime to transfer the vins and associated stamping to another car with the intent of recreating the former on the later. Now, that isn't to say it is impossible as there are legal ways to do that, but it typically involves witness affifdavits from law enforcement that was present at the time of the vin transfers who agree the said transfer was performed under the laws of the state you live in and was witnessed by their presence. This may also put your title at risk of being re-issued as a salvage, which impact the car's value in the future.
There are enough reproduction parts out there to rebuild your '70. Its just going to take lots of time and effort, and probably 5 grand in sheetmetal.