Allison also was in the game. Dan Whitney's "Vees for Victory" has the 'best desciption I have seen of the V-1710 E27 turbo-compound engine. It was a E22 mechanical supercharged two stage engine (no turbo) with a GE CT-1 exhaust gas power recovery turbine feeding power back to the crankshaft. Plenty of power - 2800 HP at war emergency conditions. Sticking point was the exhaust gas turbine was only good for 1725 deg F and that temerature was 'easily' exceeded at full power. Rather than working into 1946 or 1947 to develop an air cooled turbine that could handle exhaust from 115/145 fueled 6.0:1 compression 100" manifold pressure cylinders, they decided to turn their efforts toward pure jet and tuboprop gas turbines.
Piper106