Ask and ye shall receive.
1 Clifford was indeed in a band on the show The Jim Henson Hour. The name of the band was "The Solid Foam", and Clifford was their main singer. However, he played either a base guitar or often switched with Beard and played main guitar.
2 Clifford appeared as part of the Electric Mayhem in the TV special, The Muppets at Walt Disney World. There, the band went on what they thought of as a world tour through the World Showcase portion of EPCOT Center. And in that musical number I've been told that Clifford played the glockenspiel.
3 However, wanting my action figure of Clifford to fit in with the rest of the band, my brother painted an extra base guitar from an extra Floyd Pepper figure to look like the one Clifford used in JHH.
And the band now looks even better, what with Clifford on second base guitar and Animal banging away at the giant shoulder drum from Animal 2.
Hope this helps and have a good day.