I'll go out on a limb and say cast may be best in your application. You can run tighter wall clearance which reduces noise and wear. Weight is not a big issue with moderate cam/moderate RPM.

Goes without saying whichever you choose needs to be done correctly/carefully. Compression, wall clearance, ring gap all dialed in for the piston. If your engine guy isn't comfortable dealing with cast pistons, is he the right guy for your situation?