According to research done by bibliohistorian Jim Linderman, Justin Kent was a pseudonym of a man named Kenneth Johnson, one he used to write a small catalog of naughty books in the 1950s. Not having read Fast Curve, I can only recommend it on the strength of its primitive-but-cool cover and its Steve Bartman/Moises Alou-style meeting between a pretty girl and a first baseman described on the first page (seen below). Beyond that, you're on your own.