Slave cylinder

06 F350 6.0 Power stroke with the 6 speed manual. My clutch is slipping so I'm replacing it with a Luke clutch. Looking under the truck I see a plastic piece that I can put a wrench on, is this part of the slave cylinder? I thought it was an internal slave cylinder, if it's external I won't replace it. Any advice on changing out this clutch? I've ordered the one piece flywheel.