The analog board from a 575 has been used in Colour Classic hacks to reach 800x600 - but that's a different CRT assembly altogether. Whether it can be achieved in the 575 itself is another question.

http://www.applefritter.com/node/5200

This CC hacker tried both a 575 analog board and one from a Macintosh Color Display (M1212)

http://www.applefritter.com/node/6942

Further clues:

http://www.applefritter.com/node/4801

http://www.applefritter.com/cgi-bin/YaBB/YaBB.pl?board=powercc;action=display;num=1071502305

http://www.applefritter.com/cgi-bin/YaBB/YaBB.pl?board=powercc;action=display;num=1045165303

http://www.applefritter.com/cgi-bin/YaBB/YaBB.pl?board=powercc;action=display;num=1042249830