You're absolutely correct about Butler. My mistake for not noting him. Beall was more of a "moderate" Northeast type of Republican, though. And Mathias was a flaming liberal!
They also elected Spiro Agnew as governor in Maryland. So it hasn't been impossible for conservatives to win there. But it has been rare, which does make the state different from the South, where electing conservatives is the norm.
Well, Beall's lifetime ACU rating was 50, which was far higher than many of his RINO colleagues (some of whom quite literally were in the single-digits). Mathias was so liberal that he was giving strong consideration to switching parties by the end of his final term (in exchange for the 'Rats allowing him to continue serving as a Committee Chairman), but given that the GOP Senate had more than 51 members during his last term, he couldn't be rewarded, and had he run again in '86, there would've been no reason to reward him for switching when the 'Rats won back the Senate.
As for Spiro Agnew, Agnew ran as a LIBERAL Republican in '66 (in the mode of the previous successful liberal RINO Governor, Ted McKeldin). The Conservative in the race was the infamous George Mahoney, who managed to narrowly win the Dem primary. Horrified liberal 'Rats voted for Agnew and a 3rd party Dem liberal running as an Independent. Agnew didn't become a Conservative until the year he became Nixon's running mate following the rioting in the wake of Rev. King's death. Ironically, it was his previous ethics as a LIBERAL that ended up doing him in politically.