Please pass on my thanks to your cousin for sharing the letter, as I'm sure many here enjoyed reading it. It seems that new sources of letters and diaries are becoming more difficult to find. By now I guess most of the trunks and attics in old homes have been gone through. Some of these items are in private hands, but I cringe to think of all the trunks that were opened by people who had no interest in history and figuring a bunch of old letters was worthless just dumped them in the trash.
If you have the opportunity to visit the battlefield in the future, I imagine the visit will be all the more meaningful now that you have the letter written by your great grandfather. Thanks again!