Correct. The Pontiacs in both versions of the Challenger I were garden-variety. Though Pontiac wasn't an 'official' sponsor of the Challenger, the engines were supplied by Pontiac. One story is that they were used test-engines that had a lot of hard time on them, and an engine failure may have been to blame for Thompson's inability to make the return run and clinch the official land speed record. At the time, it's said, Thompson blamed a broken driveline part, in order to avoid casting Pontiac in an unflattering light as far as reliability.
Still, he managed to break the existing record, running 406.6 MPH in a car that was very much an owner-built hot-rod in the best sense of the word.
The Revell Challenger I kit engines are almost identical to the Revell parts-pack Pontiac engines, except for the blower drives, oil pans, and a few other small parts.