Any companies selling complete small block overdrive transmission assembles?

rear engine cross over bracket? can you expound on this a little bit?
(all the rest makes sense)
Some of the Chrysler FSM terminology is unusual and outside of the industry's usual wording.
Ma Mopar calls a drive shaft a propeller shaft.
They call the "z-bar" a torque shaft.
We all know about the Sure Grip vs Posi argument, right?
Ma Mopar does refer to the transmission mount as a rear engine mount which is a really stupid term since the engine isn't back there, it is clearly the tailshaft of the transmission.
In terms of what JBC/John was referring to, it is commonly called the torsion bar crossmember. It often needs to be modified to allow fitment of just about any non stock overdrive automatic transmission. These transmissions are thicker in girth in this area so something has to give. Some just modify the bolt in crossmember to hang lower but this is a BAD idea. It results in a bad driveshaft angle and early U-joint failures.
Many people will cut out the center of the torsion bar crossmember and fabricate something taller and wider (Welded in, of course) to allow fitment of the thicker transmissions.