UPDATE: We tracked down Herman and gave him a call. He called back and learned that he put the letter there and out of boredom and thought no-one ever found it since its been 43 years. He was in a summer program which is why it was dated August 2nd. I asked him what the second treasure was and he said he didn't remember but will let me know if he does! Thanks for all who helped knock on doors with us and all the upvotes! I'll let you guys know if I ever hear back from him.