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.
Interesting info about Agnew! I never knew he was regarded as a RINO early in his career. Yeah, Beall was better than the block of very left-wing RINOs that populated the Senate in those days. Mathias, Stafford, Brooke, Weicker, Javits, Case, Schweiker (who became more conservative after his association with Reagan).
I'm in Tennessee. We're a conservative state but we still manage to elect liberals from time to time. We were stuck with Al Gore Sr. in the Senate for three terms. Then we got stuck with his son for a term & a half, and we had Jim Sasser for three terms. These guys run initially as conservatives, then move to the left after being elected. They cast a few conservative votes when they're coming up for re-election, then shift back to the left when they're back in office. We finally got sick of Gore Sr. & Sasser pulling that stunt and voted them out, but it took 18 years to do it each time. Gore Jr. outed himself after becoming Clinton's VP.