Full time 4WD was the NP203 transfer case. Offered in half ton Ford, GM, and Dodge trucks from '73 to '79. Few ¾ ton as well. It was NEVER offered in an early Bronco. It was offered in the '78/9 Broncos.
The Bronco was built on the Dearborn truck line. So all matter of trucks ran off together. A build sheet that covers all models is very understandable.
Some of the build sheets show 360 and 390 engines and all manor of transmissions available. They were for the full size trucks on the same line, but not for the Bronco.