As one who was there, this is nearly 100% dead-on... (and that means "correct"...)Trenchy, here in the midwest of the US i don’t think you’d call the gearheads gangs but just guys.
I can’t speak to the 50’s hot rodders but in the 60’s and 70’s it seemed to be Ford guys, Chevy guys or Mopar guys. In the early 70’s street racing i loved blowing the doors off the Mustangs and big boxy Mopars with my little 69 Z28. It represented the Chevy guys very well and pissed off many of those other guys.
Corvette guys were a different breed all together.
B
Car-brand loyalty was much closer to sports-team loyalty - San Francisco vs. Kansas City, etc. - No hostile "gangs" in the urban reality or movie sense...
"...i loved blowing the doors off the Mustangs" - that means outrunning them badly...
Even later Mustangs never fully lived up to their reputation...
"...big boxy Mopars with my little 69 Z28."
Z28's were great cars, and as a devout Chevy fan I would hope that is true, but up against a Mopar Street Hemi I would hate to put a large bet down either way.
It would be fun to watch...