Water spray is only a short term solution for engine cooling. The long term solution requires larger radiators with adjustable louvers and maybe ground cooling fans.
The primary reason for fuselage-mounted radiators is minimizing the weight and length of hoses. Nothing forbids mounting radiators farther outboard on wings or even on tail booms.
Air flow around the aft end of pusher cowlings is always problematic because you need to quickly taper the cowling from full engine width to the mere diameter of the spinner. At best, this distance is twice as long as on a tractor engine nacelle.
The other problem is combining airflow off a nacelle/pod/gondola with airflow over the top of the wing root. One way to improve airflow is giving it a longer transition zone. Since this requires mounting the propeller farther aft or mounting the engine farther aft. Drive shafts are always at risk of developing bizarre vibrations. OTOH mounting the engine too far aft un-balances the airplane. Balance can be resotred by seating the pilot or guns farther forward, but that also requires a longer and heavier fuselage pod,nacelle/gondola.