The SX3 plugins would not be 64 bit and the OS would need to still support Power PC for them to even have a chance at working. They are not designed to work in C5 and I would not expect any of them to work in C5.
Personally, I would suggest either completing the mix in your old SX3 system or mixing in C5 with the new plugins (which I do think sound much better than the SX3 ones did). I’d also suggest using presets to help you save time on loading replacement plugins.