When was that anyway? I arrived in that area way back in 1966...and was kind of surprised to find Top 40 on WRKO-FM and WKBR-FM at that time. But I am certain that WLLH-FM was elevator music by that time. And then the calls were switched to WSSH with in a couple of years...And still "elevator" for many years to come...
My memory is more like yours. While I lived out of range of both the WKBR-FM and WLLH-FM signals, I was able to receive on a little table-top radio WRKO-FM in South Kingstown, RI, and yes, they were rock during my time living there; they were a simulcast during the day of WRKO-AM (Now Radio, The Big 68), then "R-KO, the shy but friendly robot, all night long." In 1969 or thereabouts, they transitioned to that awful Hit Parade '69, etc.
I remember the announcement that on June 1, 1968, the day of my calculus final, WHDH-FM was going to begin playing rock. Before I left my dorm room that morning, I tuned my radio to 94.5, and, yeah, there was rock music, but it wasn't enough to tear me away from 98.5 WRKO-FM.
When I moved to the Merrimack Valley in the early 70s, both 92.5 WHAV-FM and 99.5 WLLH-FM were playing "beautiful music", as it was known then. WSSH was still years away from its "easy favorites" format.