Hi Will,
Your guess is right. They are .30-06, and from the date, they would be ball ammo for the Garand. If they've got water damaged boxes, with the top missing, there is no collector value. Hopefully they will fire, but that depends on whether the moisture got into the cases. GI ammo is usually well sealed, so it's possible they are good, but no way to tell, until you try them.
Hope this helps.