Feasibility of swapping two MacBook Pros (both hard drive and RAM)?
The RAM speed won't be a problem, the system will detect the speed of the RAM and run it at the maximum compatible speed. Hard drives also won't be a problem. (you will want to do a "fresh" install of the operating system)

As for the RAM voltage, I think that would be a problem. I'm not completely sure though. Whatever you do, make sure you run the Apple Hardware Test and babysit the machine while its running. Chances are if it passes all the tests, you're good.