57 Chevy cars did not come equipped with Hydramatic transmissions- - - -they had a cast iron 2 speed Powerglide. There was a piece of mechanical throttle linkage that operated the throttle pressure bellcrank on the driver's side of the transmission. Are you talking about a car or a truck?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!