Complex sentence: In addition to the displacement bump, this mountain motor also gets a race-ready cylinder head with surface-milled--not cast--combustion chambers and polished ports, plus higher-lift, longer-duration cams and lighter, higher-compression pistons.
Split into simpler sentences: In addition to the displacement increased the motor gets polished ports a race-ready cylinder head with surface-milled--not cast--combustion chambers. Plus higher-lift, longer-duration cams and lighter, higher-compression pistons.