I would say that you need the stock servo horn from a revo. It is much shorter than the blue al one you have. Plus I would think that the g3r kit would use the stock 2.5 revo link that connects the servo horn to the steering linkage, but I ma not sure.
Pics:
http://www3.towerhobbies.com/cgi-bin...?&I=LXHGB1&P=7