tensioner

So I have my '04 TJ and '00 XJ. Both are coil rail motors, with no A/C. The TJ has the newer style automatic belt tensioner and the XJ has the older style tensioner. I am looking to convert the XJ to the auto style tensioner. Aside from the alternator/tensioner bracket, and P/S pump bracket, has...

Okay, this is probably a simple thing, but I'm confused about a warning on the box for this replacement pulley that says be careful of using the old dust cap. Also, what do I do with this additional little part? And this piece, I assume the side that looks like a bearing that came off the...