Dad's Manta Twin Trac (no k) in the winter of 1974-1975, when it was new and driven by California Speedway motorcycle racer Sumner McKnight. It sported a full rollcage, a rear wing, and a Kohler free-air engine. As we are finding out, the 'California Racing Team' of McKnight and the late Rick Woods used two Mantas and were somewhat factory supported by Mercury.
McKnight later ran Nascar Winston West, and started six Nascar Winston Cup events, with a top finish of 14th at Riverside in 1985.
Thanks to Jerry Schmitt for pointing out some telltale signs of the chassis to us this past weekend. Jerry rescued the Manta a while back and in 2017 agreed to sell it to Dad, who raced it back in 1980-1981.