It was mid-1978.
Both these photos were from 1978, one from earlier in the season and then one from August of that year. (Photos ripped from the Kings Island Ride Ops pre-Paramount Facebook page.)
Additionally, both Bavarian Beetle and the Ferris Wheel are in the 1978 employee yearbook, and they both have largely the same crew.
Maybe a giga dive coaster? One that dives into the ground and comes up somewhere else. Say it dives from where Invertigo is located under the main walkway, comes up on the casting office hammerheads back under the walkway and comes out back in the Action Zone area and continues its cycle.