That matches what I've heard over the years. One other was they were a California car thing.
Just for kicks & giggles, there was a topic on the NCRS.org site about a 1970 tri-power 427 Corvette engine ( designated he LJ-2 )
that never was due to production problems. One member reported he has an original tri-power heat shiled destined for this car.
If the shield wasn't going to be producction based, why would it exist as a service item even before the car was built?