The Mazda comes stock with two plugs per combustion chamber so it seems a shame to abandon the opportunity to have completely redundant ignition. Having discarded the stock EFI the stock electronic ignition went with it, so a new ignition system was called for. Crook used the empty space in the RV-4s cheek cowls for his radiators. Otherwise you will degrade the rubber oil seals on the sides of the rotors. Crook used the standard Mazda oil cooler.
Later engines have an electric cooling oil bypass valve for the rotor cooling.
This is to warm the engine up faster to reduce emissions. Failure of this valve could lead to grief. The exhaust temp is about 200 degrees hotter than in a piston engine. He fiddled with tuning the exhaust, but at the Hp he will be operating he found no significant advantage and installed an untuned exhaust. For 1986 engines or later an engine installed in the car with a turbo can be run without the turbo.