That chase scene is a great way to observed Chrysler TorsionAire suspension dynamics in action.
About 20 years or so ago, I found some comments about that chase and the orchestration thereof. NO vehicle modifications, other than to the '57 Ford that Spencer Tracy drove off the cliff. Stop the video when you get a shot of the car's underside and you'll see something of the radio-controlled steering on the car (mostly sourced from military surplus items, the comments mentioned).
I do suspect that vehicle tire pressures were maximized, though, from the looks of things. Wonder how much a modern set of radials might have made in how well the cars cornered? Rather than the quality bias ply tires from back then.
The old Ford convertible that Phil Silvers drove into an alleged low water crossing in the river is another story! Rigged to simulate a broken oil pan, but between the time the location was investigated and when the shooting happened, the river's flow increased a good bit, with additional unintended dangers to Mr. Silvers' performance.
The comments were from the grandson of the man who did the vehicle prep for the movie. When he interviewed his grandfather in later years.
Even when the movie was on tv for the first time, I liked seeing how well it made the Chryslers look!
CBODY67