As I've researched Bruce Jennings, it appears his first year in a fish was 1966.
He raced a 1966 Barracuda for Chrysler Corporation, badged as car#14or15. Before 1966 it looks like he was running the Porsches.
BRUCE JENNINGS entered the first race at VIR in August of 1957. From then until the original track closed he recorded a total of 18 entries, most in his familiar #77 Porsche. His first win came in May of 1959 when he took first place in the contest for F through I Production and H Modified. His string of top three finishes in his Porsche Carrera earned him the nickname 'King Carrera' and led to SCCA C Production national championships in 1960 and 1964. He was chosen by the Chrysler factory to drive one of the Team Starfish Barracudas in VIR's 1966 Trans Am. In 1967 Jim Hall extended an invitation to Jennings to drive his Chaparral at Daytona, Sebring and Le Mans. In his final appearance at VIR he drove his 911 to 4th place in the Porsche sweep of the 1972 IMSA race. His 911 is currently owned and driven by the Marshall brothers and based at the G&W Motorsports shop in VIR's Raceplex. His 18 entries make him the all time leader in appearances at VIR. Source: http://www.virhistory.com/vir/people/alumni.htm