B4 Motor Mount Spacer / Longer Top Shaft

[liled11]

I saw that the Kyosho RB5 is comming out with a kit to center the motor in the transmission in the link below. I was trying to accomplish the same thing with the B4 however it seems the only missing piece would be a longer top shaft. I saw that the Associated GT2 top shaft is exactly what I need but it has 21 teeth instead of 20 as is on the b4 top shaft. Is it possible to remove the gear from the GT2 top shaft and replace it with a B4 top gear? Thanks for your help.

http://www.oople.com/forums/showthread.php?t=37411