The Kissin' Cousins soundtrack LP was issued in April 1964, a month after the film was released. The Viva Las Vegas EP was issued May 13, 1964, a week before the film was released. My guess is RCA didn't want to release another soundtrack LP a month apart. 3-5 months apart was the norm. In late 1961, RCA's Bill Bullock had proposed issuing the soundtracks for Follow That Dream and Kid Galahad as a "double feature" LP sometime in 1962. This never came to fruition and both soundtracks were issued as 45rpm EP's. RCA only issued two Presley LP's that year, Pot Luck and Girls! Girls! Girls!.