im not sure if i understand exactly what you mean by top and bottom. ok the part that bolts onto the engine and has the electric motor and all, needs to be from the original ez start system.
http://www2.towerhobbies.com/cgi-bin...?&I=LXJM32&P=Z
http://www2.towerhobbies.com/cgi-bin...?&I=LXJM33&P=Z
http://www2.towerhobbies.com/cgi-bin...?&I=LXJM34&P=Z
http://www2.towerhobbies.com/cgi-bin...?&I=LXJM35&P=Z
you need all those if you dont have the original system. but you can use the handheld piece from the ez start 2 system that comes with the new traxxas nitro cars like the revo and t-maxx