are you far from an auto parts store? the tensioner should be pretty easy to find, the bare pulley, even easier.
Considering the serp. setup runs everything, I carry a spare tensioner and pulley and belt in all of my rigs. I have a small box of new parts that goes everywhere with each vehicle, that way alot of the 6.5L specific stuff is on board ready to go, rather than 2 days in a motel room and rush shipping.
Good luck!