Camshaft timing

The timing belt tension-er fell out of my vehicle listed above ESI model, 3.5L 24 valve overhead cams. The car shut down while I was driving. I need to know how to be sure my cam shafts and valves are positioned properly to reinstall the new tension-er and belt. When I took it apart the camshaft sprocket passenger side mark was right on, but the driver side camshaft sprocket was of to the left of the case marks about two to three inches, so then I lined both cam sprockets on the timing marks on the housing, but I am not sure if the valves are in their proper position. How can I be sure without doing any damage to the valves before installing the belt again? Please and thanks.