Upper pedal stop is a must, without it you could get nipples jumping out of their location hole. No throttle can be as dangerous as a stuck full throttle. Pedal spring return is best done with one of these torsion springs on the pedal fulcrum point, then there is no undue strain on the throttle cable and linkage.
http://www.lesjoforsab.com/technical...ings_id537.jpg
bob