Just make a throttle cable with a longer inner cable so the carbs won't open all the way, put it on a dyno to get it checked for output and bosh, Bob's your restrictor.
In all seriousness if "a kit" consisted of a purpose made cable to restrict the maximum output to the legal limit and could not be bypassed in normal use plus a verified output map, then it should conform and not require a whole setup of jets etc to run properly.
Just a latteral thought.