CASTLE ROCK, Colo (UPI— Carroll Shelby of Dallas, driving a red-hot Scarab, firmed his claim on the U.S. Auto Club's No. 1 professional sports car driving title Sunday by winning the 100.8 mile Colorado International race. Shelby set a new lap record for since he won a 200-mile event in April at Riverside, Calif., piloted Scarab No. 2 around the Conti nental Divide Raceway course for 36 laps in a time of one hour, 20 minutes and 42% seconds. He collected $1,920 af the $8,450 purse for the performance John Kilborn of Decatur, Hi, made it a clean sweep for the Scarabs and the Meister Brauser racing team of Chicago by finish ing second with a time of one hour, 20 minutes and 32:22 sec onds. In third place was Jim Hall of Dallas in a “Birdcage” Mas sarati. Hall was less than six sec onds behind Kilborn Shelb set a new lap record for the 2.8 mile. 10 turn course. The record time was 2.098 minutes. He beat that time, unofficially, in the time trials, when he turned in a 2:06.32 lap. Rodger Ward finished 10th in the 35 car field