wuzak
Captain
Have Rolls Royce produce about 800-1000(?) of a 'derated' version of the 'R'. The Fulmar has a large enough airframe that it could handle the weight and size of the engine, despite the added length of the 'R' engine over the Merlin - CG and w&l could be dealt with fairly easily. On 100 grade fuel it would have a continuous power rating (2850 rpm at +9 lbs) of ~1900 BHP at 9,000 ft. Military (3000 rpm at +9 lbs) would be ~2000 BHP at 10,000 ft. Note that this is for the 'R' with a 7.47 SC gear ratio.
Rolls-Royce did test a detuned R as the Griffon I (~1933). Its performance was not great, and it was abandoned.
I can't see how a detuned racing engine from the late 1920s/early 1930s would be able to have continuous power greater than the maximum power of the Griffon II using the same fuel.
I'm not sure that the higher maximum rpm (3,000 vs 2,850 for the Griffon) would be sustainable.