Carl Perkins earned his Ph.D. in rock 'n' roll long ago and now he'll get an honorary doctor of humanities from Lambuth College in Jackson, Tenn., on April 29. When Lambuth President Thomas Boyd called to talk to Perkins about the degree, Perkins asked him, "Can you graduate from college with only eight years in school?" Thomas assured him that he could, in this case. . . . There's another Kennedy wedding coming up in the fall. Kara Kennedy, 30, daughter of Sen. Edward M. Kennedy (D-Mass.) and a producer on "Evening Magazine" at WBZ-TV in Boston, will marry Michael Allen, a Washington architect. The date and site of the wedding were not announced. Kara's cousin, Kerry Kennedy, 30, daughter of the late Robert Kennedy, recently announced her engagement to Andrew Cuomo, the son of New York Gov. Mario M. Cuomo.