Does your van have the serpentine belt? If so maybe I can help, I replaced the Power steering pump on my 90 G20 a couple of weeks ago. The trick is that you need to pull the pump pulley which is pressed on to access the mounting bolts which attach the pump to the engine. Harbor Freight tools sells a great tool designed for this job for $20.00. Once you have the correct tools, remove the serpentine drive belt. You may also need to remove the fan shroud. the pump shaft looks like it has an allen socket in the center, but this is for use in the manufacturing process, and will not come out. Place the puller tool on the pulley following tthe instruction that come with the tool, and remove the pulley. loosen, but do not remove the nut on the high pressure hose connection. use a pair of **** pliers to cut and remove the crimp clamp on the low pressure hose. If your pump has the remote reservour loosen the clamp on the reservour hose also. Remove the three mounting bolts, place a large pan under the pump to catch drips, and remove the prevously loosened hoses. there will be fluid leaking all over and the pump should come free, There are two types of replacement pump sold. With and without reservour. This reservour is a metal cover that fits over the back of the pump, and should not be confused with the reomte revervour found on some newer models which is next to the battery. This reservour is held in place be two throught the pump bolts which are removed at the back of the pump. If your new pump has a reservour you will probably still need to remove these bolts and put them in the replacement pump as most are shiped without these bolts. If you replacement pump comes without a reservour pull the bolts, the reservour should pull off of the old pump and slide onto the new one. check the o rings and replace the through the pump bolts. Installation is the reverse of removal execpt that 1/2" hose clamps replace the crimp clamps on the low pressure hose, and the puller tool is set up differently to replace the pulley. Finally if you don't flush contaminants out of the system your repair will last maybe a week. www.cardone.com
has a great article about power steering flushing, read it before you start Good luck.