Yes, the UOP Shadows and all other Can-Am cars (except the Porsche 917's and the ocassional Ford powered car) were powered by big block "Chevies" The power to weight ratio of those cars will not be approached again! They would not downshift going into corners because the engine inertia slowed down the braking. They would just shift into neutral, brake into the corner, select the gear they needed to accelerate out and go like "h*ll!"
The fun part was that you could find them working on the cars in very unusual locations. Once at Mid-Ohio, we went past a Gulf station in town (Mansfield, OH) and watched the McLaren team work on their two cars in the two bays on a Saturday night between qualifying and the race on Sunday.
Also remember being at Elkhart Lake in the garage on a Saturday after the Can-Am qualifying. The Formula B's were running their race when it started to rain. Remember Denny Hulme standing next to us watching the race and commenting to his crew member that most of the cars were still on slicks. He replied that "those are probably the only race tires they have!" How true.
Those days, unfortunately, are long gone, and will never come back again. If you were there at the time, remember them fondly as I do. This was another series where it was proved that the only substitute for cubic inches is cubic money. And like F1 today, it proved that very limited rules only result in one team dominating the series with little, if any, on track passing.
If you want a good idea of the power, seach on the Brian Redman Challenge. A year or so ago, some dumb (but rich) owner of a McLaren Can-Am car let his mechanic drive it into town for the Friday night Concours. As soon as he reached the highway with his son in the passenger's seat

he decided to show the kid what kind of power the car had. Next thing he knew, it was upside down in a swamp on th side of the road. The only thing salvageable was the number plate.