The 429 had to be homologated for NASCAR in a production vehicle (which is how we got the Mustang Boss 429), but you are correct in stating that the technology developed on track could be purchased at your local dealership.
I’ve yet to find a Fusion with a V8 engine, much less one that is rear-drive.
Or a Camry with a pushrod V-8. What would a 5.7 Liter Tundra 4 cam 32 valve engine built like a NASCAR engine do to pushrod engines used now? Or a Lexus V-8 if it must come from a car. Or the Ford Boss 302 in the Shelby?