With your current set-up, the GI 4DTV is manually controlling the dish positioning and the polarity selection.
Example: To scan a vertical channel, use the 4DTV to drive to the target satellite and select channel 1 to rotate the servo probe to vertical polarity. Now set the RC-1978 to blindscan only Vertical polarity and perform the scan.
When the vertical blind scan is completed, place the 4DTV on channel 2 to rotate the servo polarity to horizontal. Set the RC-1978 to blindscan only Horizontal polarity and perform the scan.
To watch a Vertical channel on the RC-1978, switch the 4DTV to channel 1 (odd channel) for a vertical servo position. To watch a Horizontal channel on the RC-1978, switch the 4DTV to channel 2 (even channel) for a Horizontal servo position.
A pain in the rear end to manually control two separate units to select a satellite and a channel, but it is and can be done.
Better options are as KE4EST and Arion suggest, either partially automatic operation using a LNBF and your 4DTV as a mover or fully automatic with an ASC1 controller.