Considering the time and place, I don't think either man would have written an ad.
However, if we placed them in our world today, I think Jack would have somehow, very surreptitiously, placed an ad for a buddy. I think Jack was very lonely during the years he was married to Lureen. All he had to look forward to were the visits with Ennis and they were few and far between. So, I think he might have advertised for a friend, hoping that friendship would evolve into a relationship.
Ennis, though, would not have been so forward. While I think he was the neediest of the two, I don't think he recognized his own neediness, so I don't think he would have tried in any way to assuage it. I don't think he wanted anyone but Jack, and, when Jack wasn't around, he could stand it and did. He never went out looking for friendship or anything else. Just my two cents.