Hi Patricia
welcome to the forum. Have you tried to get his service records? They would contain his assignments, and may have mention of his Purple Heart (if he received one for being wounded in action). It maybe the case that he wasn't wounded on 634 but another boat, and the records would be the only way of confirming where. The other option is actually contacting the Coast Guard to ascertain the movements of LT 634, as such small craft sadly don't figure much in history books:
How to Request Military Service Records or Prove Military Service (DD Form 214, DD-214, DD214 United States Coast Guard - Home Page
good luck