I read a bunch of those including THE SINISTER SIGN POST and THE HOUSE ON THE CLIFF. Every one had essentially the same plot and phrasing, although I didn't catch onto that as a kid. Good books way back in the day.

Frank and Joe always fought crime in their neat sweaters and button-down dress shirts and always referred to their friends as "chums." Boy, that goes WAY back in years.

It wasn't until 1987 that Hardy Boys books featured any murder or real violence.