Wasn't an option. V01 Heavy-Duty Radiator was "...not available when 396 cu-in engine or Z/28 is ordered."
Appears that if an early L78 was ordered with a 410 axle, Chevy included the 4-core radiator n/c. As of the April '69 ordering revision, Chevy added a confusing note to the G80 Positraction option: "Ratios 3.73 or 4.10 also includes HD radiator." For those cars the msrp for G80 positraction is $56.90, $14.75 more than normal. V01 msrp was $14.75.
I doubt this car was built with a 4.10 axle. The radiator may have been added in the resto.
While many Festival cars are 350s, not all were. The body number of 268650 puts it early in the ordering process; virtually all known Festival cars have N268xxx body numbers.
Just putting this out there, there is no documentation that would prove this car was built as an L78.