Mad Magazine number 77 is shown clearly to Mike Hammer's left side at the magazine stand.
It was originally announced that this would be filmed in Dublin.
Mickey Spillane plays his own fictional character, something extremely rare in movies as authors usually aren't actors. In this case, Spillane was a true tough guy character type, but was not a trained actor.
The end credits have the London studio blocked out; perhaps this was so people in America wouldn't know it was filmed in England (some exterior shots are filmed in New York, but it's mostly shot in England).
According to the commentary, Mickey Spillane and Kim Tracy, who plays the nurse, got along well, as the film historian put it.