With the emphatic caveat that I am not saying the others are wrong, or that it's definitively not a tool for splicing an eye in a rope - it looks homemade, and people make all kinds of things as aids in all kinds of jobs, I do a fair share of splicing, and I have modern and historical books on the subject, and I have never seen a block or any other tool like this or any other used for splicing an eye in a rope. Fids and marlinspikes, sure. Serving mallets, sleeves, and heavers for other kinds of splices. But nothing like that thing. There are clamps and riggers' screws or vises that are used for splicing wire, because wire is just too difficult to handle and keep taut manually. But they don't look like that, either.
Typically, though, the end of a rope being spliced back onto itself to form an eye is laid out on a bench or in one's lap because it's necessary to turn it when splicing.
Also, the reason I asked about that piece above the tear-dropped shaped block is because it would get in the way. That is where the splice would be. You'd have to be working with your hands above that piece. If anything, when I look at that piece in conjunction with the tear-dropped shape block, it makes a figure 8. See how the piece above it has a rounded bottom? If something (tubing, wire, perhaps rope) was wrapped in this thing, that rounded shield would separate it on either side of it.
Lastly, different applications take different sized eye splices. You'd need several of these.
Again, not disagreeing definitively. Just my $.02.