No matter what branch of originalism you subscribe to, it seems pretty clear that it requires a pretty heavy engagement with primary source historical texts which can illuminate the original intent/meaning/understanding of the clause in question. If law only carries normative weight via its original "construction" (which I'm using as a catch-all for these three variations), then there is no substitute for knowing this history.
But I have to say: the number of putative originalists out there far, far outstrips the amount of people who I can even optimistically imagine to be such history buffs. Some originalists undoubtedly do know the history like the back of their hand -- many originalist academics, perhaps many originalist judges. But in the public arena, I am very skeptical that official adherence to originalism is matched by the knowledge base necessary to make valid originalist claims.
By itself, this wouldn't be a problem: one could adhere to originalism, and, knowing one's relative ignorance of the pertinent history, declare one's neutrality when various politically-charged decisions come down. What grounds do they have to judge -- they have no idea what their own theory is telling them the law should have said! But of course, that doesn't happen. It seems many nominal originalists do engage in bitter recriminations against court decisions they dislike, even though they exhibit little to no knowledge of the historical circumstances that would give their critiques weight.
Guesswork originalism is thus the practice of assuming what original construction is in absence of specific knowledge of the relevant history, and then stating claims on basis of that guess. It is, to be blunt, an embarrassment to the originalist project (at least when it is not called out), because guesswork originalism is rarely anything but politics and wish. They hope the 14th Amendment's original construction mandates the recognition of interracial marriage (Loving v. Virginia), but they don't know it. Contributing to public discourse in such a way is an act of bad faith -- it makes claims on the basis of particular warrants that the speaker doesn't actually know exist. Since their interlocutors (who, not being originalists, are even less likely to know the history) can't cross-check, it leads to a debate that is entirely hypothetical even as it purports to be concrete.