In the unlikely event that neither Lewis nor Dachman knew anything about gialli, they've still managed to make one. You have the murder mystery involving a black-gloved killer, an amateur detective (well, a newspaper reporter who hires a professional PI), sexuality (well, tits) and (extremely) gory set-pieces. These set-pieces are Lewis at his most extreme, and the semi-permanent retirement into which he entered after this film (retirement from films, anyway) was likely at least partially motivated by a feeling that he had nowhere else to go as a filmmaker.
The murder scenes are completely devoid of suspense, straddle a line between gross-out and (knowing) humour, and, frankly, have to be seen to be believed. But the fact that they exist in this film, and gialli in general, can be at least partly attributed to HG Lewis's pioneering work in the early 1960s.
Although it wasn't his only cinematic innovation (he also made the first 'roughie' film), I refer here specifically to his 1963 effort Blood Feast. This film is a marked failure on every technical and narrative level, yet is simultaneously extremely watchable, and great fun. It also contained several lengthy gore sequences, for which the narrative-such as it was-ground to a halt, to be replaced with spectacle, pure and simple. These were analogous to musical numbers (ones which don't advance the plot or add to characterisation, at least), replacing frothy singing and dancing with frothier blood and gristle. Although most gialli contained relatively restrained gore sequences, they routinely press the pause switch on the story so we can spend several minutes watching a young woman (or man) be menaced in, say, an underground car park. And some gialli, particularly those made by Lewis' Italian soulmate, Lucio Fulci, did indeed wallow in grisly guts and entrails.
So, HG Lewis has earned his place in the pantheon of cinematic greats, because he was willing to colour the screen blood red in unflinching detail. Some of the films he made between Blood Feast and The Gore Gore Girls, notably Two Thousand Maniacs!, did attempt to incorporate a tense(ish) build-up before the gory pay-off, albeit with the filmmakers' tongues never straying too far from their cheeks. But still, is it a coincidence that the Feast was followed less than a year later by the Black Lace? Possibly, yes. But even if it is, we can conclude that an air of permissiveness and experimentation must have been blowing towards the filmmakers of the early 60s, and it was Lewis who felt it and channelled it first.
The Gore Gore Girls doesn't warrant too much scrutiny in and of itself as a giallo. The plot is razor-thin, and frequently nonsensical, the gore effects are so over the top that they're impossible to take seriously (which was, as noted, the intention), and the direction, while not quite as perfunctory as that of Blood Feast, is hardly Bava-esque. In fact, you'd be hard-pressed to think of a less-stylish giallo (possibly The Bloodsucker Leads the Dance, or one of the later SOV ones). The music, far from driving the action in a Goblin-esque manner, is made up of library cues which often counterpoint, rather than complement, the on-screen action. This, as with the clunky plotting and humour, may have been a deliberate choice of Lewis, who, was too clever to be unaware of his (many) failings as a filmmaker.
In short, even if you're a giallo completist, you can probably leave this one off the list. If you're a HG Lewis, or American trash cinema, completist, you've probably already seen it. For everyone else, unless you've a weird thing for breast milk, there's probably not much to see here. But you should still doff your cap to ol' Hersch. Unless you don't like gore, or mail fraud (Google him). In which case, on you go.