Not as simple as just flywheel and carbs.
Main differences between the BR and the B are;
Externally - BR used different flywheel and magneto, dual carbs with progressive linkage, drip oilers, cylindrical gas tank, and choice of propeller
Internally - BR used two-ring pistons with aluminum rods, the crankshaft is drilled for better oiling, and I'd leave it up to Jim Ross to tell me whether the racing crank had bigger journals for the upper & lower bearings or not.
While I'm thinking about it - what prop(s) do you have on your motors? They are ID'd with letters and numbers on the prop hub.
Standard prop is usually 9 inch diameter X 14 pitch
Racing prop normally at least 15 pitch and I have seen one marked as a 16 p.
Brief synopsis of Chief HP ratings - some books show the service motor rated at 14 HP, but 11 is more realistic.
14-plus horsepower rating should only apply to the BR. Unless they actually dyno'd motors, I doubt they knew for sure if it was putting out more than 14 HP or not
In 1931 the service Chief was sold only to Montgomery-ward to be re-labeled as a model 500 Sea King. These motors were given a very generous 15 HP rating, even though it was the same motor as the 11 HP service model B. All model 500's marketed in 1931-32 were rated at 15 HP
in 1933 the NOA rating system was implemented, resulting in a downgrade of the model 500 Sea King from the advertised 15 HP to a more honest 11 HP.
Hope this helps.