according to the prm website the 260 should handle a JP3 even on a heavy commercial rating. i would be more tempted to fit the 500 though, especially if the engine is worked hard or a lot of river work is likely. the prm 160, which was replaced by the 260, in wyrd has been rebuilt 3 times in 20 years and still has a habit of dumping all of its oil into the drip tray under the engine with a compete loss of drive!! not good on rivers. the other thing to be careful of , is the minimum engine speed that prm recommend for the gearbox, a JP3 might have to run a bit more quickly than you may like for the gearbox to work correctly. hope this helps
Tom