3.3 revo front and rear center shafts are the same lengths. The 5456 will work perfectly. Keep in mind that even though you have the gmaxx single speed conversion, the tranny shaft is still the same lenght and 6mm in diameter. Just make sure you also buy the 5458x yokes.
http://www3.towerhobbies.com/cgi-bin...?&I=LXMJG9&P=M
Or you can go to fleabay and buy them:
http://cgi.ebay.com/NEW-3-3-T-MAXX-C...QQcmdZViewItem