Based that I have both motors the conrods are not the same you can use the Evo3 piston/sleeve/conrod in the Evo 4 but not mixed matched the sleeve is the same piston as well but the conrods are slightly different in height.
as for the Sirio power clutch it's all in driver preference the power clutch has the same feel for those that have tried the sp kyosho clutch or 2D/4D clutch set up is very similiar but the 3D to the power clutch settings are totally different. cranking down the spring tension on the sirio to 1.2 is to extreme the sirio spring height is taller than the kyosho spring & my spring collapsed very quickly I normally tighten it down from .5 -.8 range very smooth shifts spools up very quickly. Im very happy with it I also installed the Orion spring on the power clutch to make it a little more aggressive & shaved a 1/2 sec in lap times