Experimental Plymouth..
Yep. "pretty Ugly", was the terminology. They were right. I don't think Corvette's popularity would have been challenged by that particular car.
...and, Yes, I do remember it. I was about 10 years old, then, and a Chrysler fan, too. The "early" Hemi's from Chrysler, Dodge and DeSoto affected and infected me, but I doubted, even then, that the Corvette was "in trouble" due to this car. The 1957 thru 1962 Corvettes were gorgeous, well balanced, and well powered with the early small blocks. Even Ford gave up after a 3 year run of 2 seater competition for the Vette. The 1955-57 Thunderbirds are classics 2 seaters now, but no competition for the contemporary Vettes of the day. 1958 Saw T-Birds going to 4 seater Coupe body style, leaving the Corvette as the only true American 2 seat production sports car.
I remember being disappointed that Chrysler never took that segment seriously enough to honestly give Corvette a run for it's money. 1960 was the time of Chrysler's Polysphere small blocks. I'd always imagined a Chrysler version of the a Corvette Roadster powered by a 277 or a 301 Poly engine. There were several, so called "experimental cars" that graced the pages of Hot Rod, and Popular Mechanics back then, but never a serious effort from MoPar.
Whether they viewed the Corvette as too much competition, or just looked at the segment as a low production area of a "niche" segment, is still debated today, but they never took a real step to enter into competition for sales in that segment, until much later with the advent of the Viper, and they proved, beyond a shadow of a doubt that they can, indeed build a 2 seat super car. Just think of how easy it would have been in 1960 to build a 2 seat sports car before the segment gained "super Car" status.