Keep in mind that on Marlo's car dual blower belts couple the transmission output shaft to the intermemiate shaft and vice versa to the front differential if they run the front engine only. They can also drive the rear differential using this same intermemiate shaft.
This may or may not dampen the "hit" at a gear change.
The rear motor is a different story.
It's transmission drives thru a belt coupler directly to the rear end and so lack's the possible benifits (?) of the blower belt coupling.
The coupler allows the intermemiate shaft to drive the rear differential with or without a rear motor.
This is a lot easier to understand if you have a blueprint in front of you like I do!
Bob