The Griffon engine peaked at about 3500 Horsepower Most of the single RW4360's were 3500 to 4500 Horsepower and that double 4360 would have to be a real beast it would be interesting to see if the Counter rotating Griffon prop could effectively use all that Horsepower ?? Maybe a prop from the Russian TU-94 Bear if one could be obtained . But then prop diameter may become an issue ?? But that would sure give WWII fighter an awesome rate of climb .. The only factory single engine airplane I know of to use the 4360's was some of the Martin Maulers ..