It wasn't a class car, just a regular bracket car.

The moroso chart shows 682hp for 137mph, with an ET of 9.77.
His car left better than a typical car running those numbers, which is why the overall ET was better than the speed would indicate.
The moroso chart shows 138.5mph to run 9.68 but the motor didnt have enough top end pull for that.
Also, keep in mind that's a good air day.
Typical speeds were more in the 135 range.