Design was later than RE 2005 and it was started because of the lack of DB605 power units. The RE 2005 was hence reengineered with an italian power unit, namely the Isotta Fraschini Zeta RC24/60.
That unit was a 24 cylinders engine, with a "X" layout, basically two air-cooled V12 engines.
The air cooling was the major issue for the engine.