MSG Golem and now this--two Jewy stories in a row for me to sink my teeth into! It's like Hanukkah, minus 6 nights. Those were the nights when I got socks anyway.
I generally enjoyed this story. It is light in the magic department and he does skate past the plot crisis/decision point between the gangsters pretty easily; but then the gangsters are only part of his problem. The bigger problem, to me, seems to be his uncomfortable immigrant/native position, that identity crisis that you find in something like Portnoy's Complaint or Call it Sleep.
Except here, the crisis isn't just Jewish/American, but magician/rabbi (two professions orbiting around books and figuring out rituals) and magician/gangster (two professions on the fringe of society in their own ways). The central magical metaphor of "balance" seems like a good fit here, since the solution he finds is balance: satisfy two competing gangsters, while also satisfying an ethical call from the community and/or a version of his past self he sees in Goldbug (depending on how you want to parse that).
(Also, I like the story because now I get to drop the fact that my great-grandfather's saloon is listed as a gangster hangout (one of many many) in Albert Fried's excellent The Rise and Fall of the Jewish Gangster in America.)
Added: All that positivity to the side, I wish the story had gotten a little more specific about the magic being used as well as the book that's passed to the dad. As a kid interested in the weird side of history, I tended to associate alchemy with Christian and Christological magic; imagine my surprise to discover later that there was a fair bit of Kabbalah in alchemy; and that while most alchemists weren't Jews, a lot of alchemists were interested in Eastern (Jewish/Arabic) sacred/magical writing. So what book was it? Just the Zohar or the Sefer Yetzirah or something else? (Maybe something non-Kabbalistic at all.)