If you look on pg. 55 of "American Sports Car Racing in the 1950s" by Michael T. Lynch, William Edgar, and Ron Parravano, you'll find a photo (from 1951) of this car, identified as an MG-TC with a flathead Ford V8-60 engine.  Phil Hill is driving! 

The driver's helmet in this photo looks different (slightly) from Hill's helmet in the book's photo, but this photo is too blurry for me to say for sure that this ISN'T Hill driving.

What was the "Jr" class?