The pier repeatedly seen in the background by the beach is the Paradise Cove Pier in Malibu, CA. It was torn in half by a giant El Nino wave in the '80s.
When Ethel and Mr. Grant meet in the roadhouse, the exterior sign says "Jefty's Roadhouse"-- a stock shot from Road House (1948) with Richard Widmark as "Jefty".
Together with The Fast and the Furious (1954), this was one of the first films to be distributed by the American Releasing Company which would later become American-International Pictures.
The monster in a rubber suit was performed by a female, Norma Hanson. The only known instance of that casting decision being found.
"League" is an outdated unit of distance measurement, at sea it is equivalent to 3 nautical miles or 5.56km.