It would be easy to knock-off the old chapbooks. I don't know if it's been done, but any printer could easily make convincing copies of most of those early chaps (with the exception of mimeo titles like Confessions of a Man Insane Enough to Live with Beasts). But something like It Catches My Heart In Its Hands...even at the high prices you could get for it, it would be a monumental task to recreate that book. I don't think that anyone who would be interested in a con like that would have the resources (or time) to do it. It would have to be made by hand, just like the original, to pass as authentic. The production costs would be ridiculous, and a sudden influx of lots of brand-new-looking copies would be suspect, to say the least.
If you had the talent and resources to do it, it would be interesting to make a facsimile of It Catches My Heart In Its Hands, plainly mark it as such, and sell it for $149 or something. You might be able to do that. But still, it would be quite an undertaking (and you'd probably lose money).
But as fraud, there's no need to bother with the Webb books when something like Flower, Fist and Bestial Wail sells for considerably more, and would be much, much easier to fake.