Virtually the entire story "seems" to be a myth. Seemingly made up by the son, who works at / runs a video promotions company.
A Mopar expert that talked to the son and also inspected the car before it's restoration states that there was never any rumor back in the day of it being fast, and there is no evidence the car was ever modified from stock.
https://www.youtube.com/watch?v=V2LjOvcnBFU
Essentially it's a stock Hemi Challanger, which would have done a low to mid 6 sec 0-60, and a quarter mile in the mid 14 second range.
The original owner was a cop that never hung out in the car scene, but instead would go out for a bit of a drive, and then come back home. There are no reports from back in the day of it "Ruling" the streets, or being feared, or winning or even participating in a race.
But kudos to the son for making a video about it and getting Hagerty to hype the car up before the sale. All that effort got him an extra $800k over book.