70 Duster 5.7 Hemi/46RH

The 3 pin connector on the main case is for LU/OD controlled by the PCM. This year model is mechanical governor, so wouldn't apply here for PCM control. This trans came from a 4x4, you picked up a 2wd housing. So the speedo output is off of the tcase from the Ramcharger you got this from. Do you know what year this OD housing came from(2WD)?
There are specific year model 2wd cases that have both ports, for output speed and speedo. Very specific year models around 96-97 when Dodge transitioned to tone rings on the rear axle. The OD housing and output shaft are specific for a speedo driven unit.