While I grew up in the 50’s and into the Muscle Car era, I never heard of any American Made V-12 engines. (I was more into aircraft than cars.) GM however did build some V-12 industrial / heavy truck engines. If you’d like to read a short article, check out this Engine Labs article. (You can also follow some additional links from there.)
https://enginelabs.com/news/flashback-friday-gmcs-monster-702ci-v12-twin-six-engine/