I have a pair of GTX 465 unlocked into GTX 470s, do yourself a favor if you have an unlockable board get yourself a voltage modable BIOS. The unlockable boards have 10 memory chips. I've been running my setup for 2 and a half years, it has been stable with the exception I have to bump up the voltage slightly to 1.02 Volts to get it to run totally stable. The EVGA superclock BIOS are a solid bet. I would say its worth the risk at this point in time, I saw a huge gain going from 352 shaders to 448 shaders.
*Edit* My cards are the PNY Verto cards with the black boards.
You cannot unlock 460 cards to 470 cards as they are a different chip entirely. Some of the GTX 465 cards are 470 cards that didn't pass on standard voltage, but with a volt modable BIOS for the card they work just fine and don't really require a huge bump to work. You could get a voltage modable bios for your 460s which will likely allow you to overclock your cards but that is about all that you can do.