I am truly having a hard time seeing any evidence of a graft on the large trunk (on Homeby's tree)
Yeah....me too. I'm a newbie but I'm confused. Wouldn't the graft be at the very point of the V if the smaller trunk is indeed the rootstock? Am I understanding right?
The graft would almost 100% definitely be above the point where the smaller branch attached to the larger (if it were below, you would have the graft well buried underground and tree would not be healthy or happy). Commercially grafted trees in Florida almost alwats have the graft within the first 12 inches of the trunk, usually around first 6-8 inches or so. I see nothing in the two pictures you posted that resemble the evidence of a graft.
Maybe post direct pictures of the first 12-15 inches of the larger trunk. That would give a better determination.
To me, from what I see now, it looks like a seedling (but I cannot clearly see the lower part of the larger trunk).