the engine ressembles the Wright R-2160 Tornado, a liquid-cooled 42 cylinder radial. It was proposed to the AP-18, who would happear as the XP-69. It also had the engine mounted behind the pilot, driving contra-rotating propellers. Seem familiar?
from 'the Thunder Factory', joshua stoff, pages 39-40:-
'Republic's AP-10 (the _original_P-47, not the 'Jug')...would be powered by the 1,150hp Allison V-1710-39;...
Republic also proposed a similar but more advanced version, the AP-12 Rocket...which featured a buried Allison engine driving two contra-rotating propellors...'
though i agree, the picture posted shows an engine that doesn't look like a vee type engine, too many exhaust pipes.