I don't have your answer, but I found some links that will at least help you get the bolt out and in your hand. As it turns out, the marauder site has a lot of info on your gun. Maybe the path to the firing pin is clear when you can inspect the bolt.
Instructions:
http://marauder.homestead.com/files/RossiDis.html
With pictures:
http://www.leverguns.com/articles/ta...ield_strip.htm
Parts Diagram:
http://marauder.homestead.com/files/Rossi_92_Parts.htm
I think the snap caps should come out of your son's allowance.
Good luck!
Tom