Follow the same procedure as you did to change the water pump. Remove the timing belt, replace if necessary. the Align all of your timing marks. the are on the two cam gears and the crank gear. go to
http://www1.autozone.com/images/cds/...3d8010c02a.gif
this is an image of the location of the marks. also make sure when you put the belt back on that none of the gears move Try again. also keep the tension on the "Tension Side" it is depicted in the picture.
I had the same problem when i did the water pump/timing belt on my 89GC
You can also go to
http://www.autozone.com
then on the left Click Repair Info ->then Vehicle Repair Guides and follow the steps to choose your guide for you vehicle (ie. Year, Make, and Model)