After getting the wrench and discovering that fixing the belt would probably involve either taking the reservoirs off completely (which would then still be in the way), or putting the car up on ramps to get the tensioner from below, I decided to drive the van 1/4 mile down the road to a garage and have someone with a hoist and spare time on his hands do the job.
As it turned out, the tensioner was bad anyways, and that's definitely something I wouldn't want to bother with myself.
Thanks for all the advice, folks.