Gary:
You have everything you need....the second spring on the shaft is optional.
A piece of advice when you mount the vertical heim joint tab on the top of your footbox: Be sure to use a piece of steel plate that is roughly the same size of the tab for a backing plate for the tab. Doesn't have to be as thick, but the idea is for it to spread the stresses on the relatively thin walls of the fiberglass as evenly as possible. This particular mounting point takes a lot of abuse from the throttle mech, and it needs to be done very carefully. I even went as far as to fashion a thin rubber gasket on the reverse (interior). This gives you a tiny bit of "give" and takes some of the pressure off the fiberglass wall.
Good luck.
Bud