The best way I know of is a stop , usually at the carb on the linkage.
But a friend ran super comp with some success using a bolt in the foot feed , preventing it from going wide open.
Easiest and cheapest.
A restrictor plate would sure work.......I have heard good things about using them , but they would run a few more bucks.
Over at moparts , Mr. Peabody made a simple stop that went on a carb stud and worked like a champ. There is pics in some of his replies on the same issue.