The way it nearly came to the US is interesting, though. Back then, GM North America was a very different place than GM Europe, and it looked like there was very little interest in bridging the gap, unlike today. But after GM bought a 50% stake in the Trollhattan trolls, the General was now burdened with the problem of attracting more than devotees to an aging lineup at dealerships. The solution was to sell the Calibra to Americans through Saab dealerships, but badged as a Saab.
GM retains an engineering centre at Millbrook in the UK and is no stranger to tuning cars there, because it knows that British road conditions are different from those elsewhere. So whereas Opel Corsas, belying their German engineering origin, will apparently have greater straight-on stability to their steering, UK cars get a different power steering tune (electric assistance makes that much easier).
There were two distinct generations of the Kadett B: 1966-1967, and the 1968-1973. Bob Lutz had a hand in the key feature that distinguished the two. The torque-tube/leaf-spring rear suspension was replaced for 1968 by a coil-spring and control-arm set-up, designed to both improve ride and handling, especially in reducing the Kadett’s tendency to tippiness. Bob had recently arrived at Opel, where he mentioned that the Kadett had a bit of a rep in the US for being a bit tippy, especially in a J-turn maneuver. The engineers told him that the new rear suspension (seen here in this picture) would eliminate that, and invited him to see for himself. The result is self-evident (full story here).