1966 dart commando 4 speed id

I don't have precise info but subjectively after 50 yrs of sampling I suggest 273 4bbl A-bodies, Barracudas/Valiants/Darts in 1966 were likely 7.25 rears from early in production. By late 1965 build dates the 8.75 started showing up in 4spd cars but still inconsistent. I have never seen a true factory 273 4bbl automatic with an 8.75 in 1966. I've seen factory 4spd 273's with either 2bbl or 4bbl motors with 8.75 or 7.25s. That's an observation based on lots of sampling but no source data from the production side. All I have to offer, for whatever it's worth...