The Advance Adapters 6R80/10R80 to Atlas Adapter (P/N 50-3900) is built for the Ford 6R80 automatic transmission, found behind everything from the 3.7L V6 up to the 6.2L V8 in Ford trucks and SUVs from 2009 to current. The 6R80 weighs about 215 lbs and is rated for 590 ft-lbs of input torque. Ford's 10R80, released as a 10-speed upgrade in 2017, shares the same bolt pattern and output spline as the 6R80, so this same adapter kit works for both transmissions.
This kit is designed exclusively for the 4WD version of the transmission, and it uses the factory bolts to fasten the adapter — Advance Adapters specifically flags the bolt at the 6 o'clock position as one to double-check during install.
Important spline note: the Atlas paired with this adapter must be equipped with a 31-spline input, but the casting doesn't use Advance Adapters' standard 31-spline input — it requires the shorter 31-spline part (P/N 300110A, or assembly A31S). If you already have an Atlas with the longer standard 31-spline input, it can be shortened to fit this application instead of sourcing the shorter part separately.
Adapter length is 3.625". The crossmember rubber mount for this casting is P/N 716655; for a Ford Bronco install, Advance Adapters offers a complete crossmember support kit to the frame rails (P/N 716040).
Bronco-specific note: if you're installing the Atlas in a Ford Bronco, Advance Adapters recommends the shift kit made for the Atlas 4-speed — its longer shifter assembly (P/N 344004) is a better match for this transmission's length than the standard shifter.