I'd just get 4 ball nuts, 4 ball cups, & a throttle linkage that's threaded on both ends. Also might want to change out the servo arm to something that has a hole on each side. Maybe like this:
http://www3.towerhobbies.com/cgi-bin...?&I=LXXRA5&P=7
Could also just use 2 ball nuts & 2 ball cups, then put a Z bend in the linkage.