Bobby Frankel has decided to send Mast Track to Hanshin for the Dec. 7 Japan Cup Dirt after all. The Hollywood Gold Cup winner, trained and owned by Frankel, was scheduled to leave Los Angeles International Airport on Wednesday for the 1 1/8-mile Grade 1 contest, a day after the Rick Dutrow-trained Frost Giant left New York for the same race.\nThose two will be joined in the $2 million Japan Cup Dirt by the New York-bred Tin Cup Chalice, who has been in Japan since last Thursday.\nRiding assignments for the four American horses running in Japan on the next two weekends have been completed. Tin Cup Chalice will have regular rider Pedro Rodriguez aboard. Cornelio Velasquez will take the reins on Frost Giant, while Garrett Gomez will ride Mast Track for the first time.\nIn this Sunday's 1 1/2-mile Japan Cup at Tokyo Racecourse, the Neil Drysdale-trained Marsh Side will be ridden by Javier Castellano, who was aboard the Gone West 5-year-old for the first time when he won the Canadian International on Oct. 4.\nPrado, Garcia to bear Stars and Stripes\nEdgar Prado and Alan Garcia have been selected by the Japan Racing Association to represent the United States in the World Super Jockeys Series at Hanshin Racecourse on Dec. 6 and 7. The four-race contest will consist of two races on each of the two days at Hanshin, near Osaka, on the weekend of the Japan Cup Dirt.\nJoining Prado and Garcia among the foreign contingent will be Ireland's Johnny Murtagh; Ioritz Mendizabal, a Spaniard who rides in France; Andrasch Starke from Germany; Craig Williams and Blake Shinn from Australia; and Australian Doug Whyte, who will represent Hong Kong. Seven Japanese jockeys will be selected at a later date. \nFor the 41-year-old Prado, this will be the seventh time he has competed in the series, while Garcia, 23, will be making his first trip to Japan. Williams, the defending champ, will be making his third appearance in this 22nd renewal.