I guess you would need the Escort coupling & shaft
Would imagine that the Sierra coupling has a spline one end & a triangular bit at the other .... Better suited to joining the extension shaft to the exhisting Sierra triangular lower steering column ??
Not 100% sure on that though .... If I were to have a gripe with Rally Designs website, it would be that there is not enough product information & the images could be larger/better quality
To do a real fair dinkum job, I suspect you'll need, 1 X Escort coupling, 1 X Sierra coupling & 1 X Extension shaft ( A quick call to RD would confirm this ) .... Soon starts to get expensive
If it is of any help to you James,
I belive I have a spare, original Sierra rack coupling here that is still serviceable.
Just need to double check the spline size.
