Well, a friend tried something WAY more interesting (and risky)...
He soldered a PPC740. It's totally compatible with the 603p (voltage, data,
setup, everything). The problem is that without any BGA equipment, the
soldering was not done properly... It worked, crashed all the time and
finally the chip was fried. This wasn't up to any voltage problems.
Now, if anyone could try mounting a 740 with the proper tools...