Not really, A BoB Spit used a Merlin that was allowed 880hp for take-off. It was allowed 2600rpm and 6 1/4lbs boost for climb.
The Merlin XII in the Spit MK II was somewhat better.
The Allison in the first British Mustangs was allowed 1150hp for take-off. It was also good for around 1040hp at just over 14,000ft?
Merlin III was good for 1030hp at 16,250ft (both are without RAM)
Sorry, A Merlin III in an 8,000lb aircraft is not going to give sparkling performance.