There was an old rumour (or fact..) that some guy replaced the 603 with a G3 and it work for a few moments or something. Would be cool to do it but at the price of this boards noone's gonna try. There's an italian company that can do BGA replacements, you just have to send them the stuff. The name was ATE I think, don't know if they still do it though...
It still probably wouldn't be such a breakthrough because the memory contorler on the BlizzardPPC sucks...
