I am not sure those value can be applied to the Hurri or the Spitfire.
Does it include compressor neg torque (some said that it was pumping out 25% of available Pow) and the prop gear box losses ?
Modern turbin are quoted in Shaft HP, value that does not include gearbox etc...
The 240lb mass does not shock me. We can compare that to the force generated by the portion of the wing fitted with the aileron let says 1/3 of the wing area -> 7000lb/3 = 2300lb = 10 time more
~S!