I always find it a pleasure when we see odd pairings like Jerry and Kevin or Frank and Richard, etc.
I think I've talked about this in this thread already, but it seems like Frank and Richard never really had any duos on Sesame Street, and it was rare for their characters to have one-on-one pairings, though the opposite is the case with The Muppet Show.
And you could say that Jim and Kevin were kind of an honorary duo in the '80s, with Ernie and Hoots being teamed up a few times, Kermit and Elmo teamed up a little more, and Elmo also appearing at least once (under Jim's performances) with Ernie and Guy Smiley.
I wonder when the last time was when Sesame Street did a segment with Jim, Frank, Jerry, and Richard. Even with all four doing the Twiddlebugs, the last few with Jim had Mama Twiddlebug performed by David Rudman instead of Frank.