The rings do not seal anyhing,however, they do keep the manifold lined up with the head intake ports.(necessary for proper air/fuel flow into the combustion chamber.
If this truck HAS been sitting for 15 years, it will probably have some stuck open valves and this would cause the engine to not run if there were more than a few stuck!!!
The steel ball will be there,may be covered with crud.Take the inspection cover off and turn the flywheel. use a flashlight or a drop-light.(if the ball is not there, there will be a hole where tha ball was.
Have you done a compression test on the engine?
THREE things need for an engine to run;
1. fuel
2.compression
3.spark
(all three at the proper time and place)

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
-
-
Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!