Is this correct?
Yes, and no, both... They are the same logic board, and most of the components are the same between the two, but the PPC has some additional stuff for handling the PPC chip, and uses a different EEPROM system.
If so, does that mean I can turn my Cyberstorm MKIII into a CyberstromPPC just be getting my hands on a 604 and plugging it in? Somebody please let me know; I'd LOVE to have a PPC card but not at the price everyone seems to be asking for it.
AFAIK, No. You'd need the PPC, the assorted surface mounted components (fairly easy), but you'd also need to force a different flash on the EEPROM and a few other things, according to a different thread on here.