The increased hp in 1953-1955 Corvettes was probably due to the dual exhausts and the three one-barrel side-draft carbs.

In mid 1954, the 235 Corvette's hp increased from 150 to 155, due to the use of a higher-lift 261 cam.

I'd bet the hp in any of the 235 Corvette engines would increase somewhat if an 848 head was put on one. People who put the higher-compression 848 head on a 261 report an increase in hp.