Here you go James
Perhaps this picture will help
Bottom of the picture shows the steering link assembly as fitted to the Sierra.
Part A fits to the end of the steering shaft ( Wheel side ) & part B fits to the steering rack.
At the top of the picture, you'll see an extension I made by simply cutting part B in half & extending with a piece of thick wall tube .... Bit crusty now but it was only made as a temporary thing to allow me to move my build about & sort out any clearance issues
Now here's the big if.
Assuming the Rally Design Sierra group 4 coupling has a triangle on one end & the other end has a suitable spline to fit the Escort rack !!??
You could do away with part B.
Cut part A in half & extend to the length desired.
You may have to remove the flat tang from the end of the triangular peice in order to engage it into the RD coupling if it proves to be suitable for the job.
I hope this helps to make things a little clearer for you