Earlier this year, we were testing a Wilier Cento Uno with Campy 11. Couldn't swap in our SRM crank, and our PowerTap SL wheel had Shimano splines on the cassette body. We called Saris and they sent us the conversion kit. Our kit came the way both come, with a different cassette body, freehub seals and two spacers. Spacers!
When we were finished taking a 5mm Allen key to the non-drive side axle and a 17mm cone wrench to the drive side axle, swapping bodies and inserting spacers, we'd have to re-dish the wheel. Oy! We needed our power! So we finished the conversion by tightening down the 5mm nut and the 17mm nut and then took a look at the wheel dishing. Maybe our initial dish job was off, but when we reassembled the wheel, the dish was not perfect, but really close. We left it. Your experience may vary.
The CycleOps PowerTap SL Freehub body is designed to work with PowerTap hubs built around a 12mm axle, so the older wireless SL, current wired Comp, the wireless Elite +, and Pro+. This body is made from aluminum, which is how the SL and Pro+ come stock. The stock body on the Elite+ and Comp hubs are made from steel, though the steel body can be swapped for the alumimi, and vice versa. The kits come with a freehub body, freehub seals, two spacers, and instructions to convert from Campy to Shimano/SRAM and vice versa. You'll know the new spacers from the old, as one set of spacers are aluminum, the other steel. You don't need to re-space the cassette for Campy 11, as you will with some hubs. There is a different kit for PT hubs with a 15mm axle. If you feel the axle and cassette ratchet need greasing, you may apply "2 grams of high quality freehub grease to the ratchet ring." We take this to mean anything thick; they recommend Kluber Isoflex and Dupont Krytox. It's been our experience that lighter oil is best for the ratchet mechanism and the pawls. Something between Phil's tenacious oil and mineral oil is probably best for the ratchet mechanism as they won't congeal over time or in the cold as can happen with thick grease. Claimed weight is 85g.