An attorney will tell you that without serial numbers being specifically listed in a living will, they are not part of the estate.
"Let's step back, a minute here. The guns belong to Friend. Texas Jack has told us that Friend let him take them for an inspection period. We know that Friend did not GIFT the guns to Texas Jack. That's all we know.
Texas Jack may not know about any living relatives, but the man may have left a will. Friend may have thought of giving his stuff to his favorite charity or church. Who knows? The guns ARE part of his estate. I'm not aware of any law that says only property with recorded serial numbers is property of the estate. (Imagine the chaos if that were so.) Now, what is part of the estate and what the administrator is aware of are 2 different questions. But I tend to believe a falling tree in the forest still makes noise even if no one hears it.
I think we all know the right thing to do, which is to contact the administrator of Friend's estate - after he passes - and alert him or her to the existence of the guns and make an offer to purchase them for an agreed upon price and comply with the legal transfer requirements if you buy them.