There is an ad on Facebook marketplace describing this Warner T-10 as a Chevelle transmission. I think its probably out of an AMC Javelin. Maybe someone here is an AMC fan and would know for sure.
https://www.facebook.com/marketplace/item/389938956017059/
Certainly no T10 in a Chevelle ever as you stated. Also, that bellhousing looks strange?
1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
Hanover, OntOntario Rodders Forum
The ad is reposted with a different description.
https://www.facebook.com/marketplace/item/368345774793787/
Paul