Let's assume that the drawing you are working on is the left unit.
Label it left unit.
Place a reference point (circular) at the outside corner on the right side.
Copy by saving the drawing as a new plan labeled right unit.
Reverse the plan so that the common wall is on the left.
Assure the reference point is in the matching location for the left unit.
Use the copy to clipboard command and select the entire right side unit.
Go back to the left side unit drawing.
Use the paste from clipboard command and the right unit will be place immediately adjacent to the left.
Use the move block command and select the right unit and move it over one inch.
Use the keyboard arrow to move the specirfic distance.