It occurred to me that the Whirlwind probably featured in that excellent series of publications “Aircraft in Profile”. Looking it up I find that apparently the government considered re-engining the Whirlwind, not for performance reasons, but to eliminate a production bottleneck with the Peregrines. The idea was rejected because the aircraft “was too small and its entire layout unpromising” (“British War Production” , HMSO). That seemed to imply a larger engine such as the Merlin was in mind, but the idea was rejected as impractical.