What size belt would I need to bypass my power steering pump?

They didn't install that engine in an application that didn't have PS so there is no real number to go by. What I would do is take the old belt. Cut it. Then wrap it around the pullies like the yellow line in the second pic. Mark that length. Take that to the parts store. And get a belt as close to that length as possible. The idea is that running it on the idler should make it short enough that when you route it like the first image with the red bypassing the PS pump, the tensioner #8 will hold it tight enough that it will work.
The OE belt is a 6 rib 103-inch belt. I suspect you will be closer to an 86� 88-inch belt but never measured the run around the PS pump. Now this is for one with AC. Without AC (image 3) you will probably have to route the belt like image 4. However, that is going to cause far less drive to the water pump so you will want to keep a close eye on the coolant temperature. For it you would still do the cut and measure, but you will want to move the tensioner out so that you get a belt that will stay tight when it moves back into place.

It shouldn't hurt the van, but it's not going to help your arms any. Once you get up to speed it won't be as bad but anything in slow traffic with turns is going to be a workout.