I mentioned this in the blog and Eric replied in the comments, explaining that Kantor was actually a well-resepected author at one time. I found that hard to believe, but since Eric was a professor (and actually spent a great deal of time riding busses on Diversey street) I bowed to his wisdom and assumed that this novel was just a rare moment of badness for Kantor.
But what do I find in the August 18, 1928 New Yorker book review section?
ANOTHER book against which insomniacs are warned by the publishers with considerable justification is MacKinlay Kantor's "Diversey," based on the activities of Chicago's gangsters and their corollary network of machine guns, gin-crazed girl friends, and crooked politics...That makes it sound a lot more interesting than I remember it, but I suppose I'll have to go back and try to read it again. The reviewer genuinely likes the book, and though the section is no longer written by Dorothy Parker, he-or-she seems to have pretty good taste.