Rear arbs from the Sierra mk2, Escort Cosworth, Granada mk3 and Scorpio are all the same fitment but different diameters:
Sierra XR4x4 - 14 mm
Cosworth 2wd - 16 mm
Cosworth 4x4 - 18 mm
Escort Cosworth - 22 mm
Granada Mk3 24v - 18 mm
Scorpio - 20 mm
Scorpio 24v - 21mm
Front calipers are the same for: Cosworth 4x4, Escort Cosworth, Granada 24v, Scorpio 24v and Mondeo V6
Rear calipers (solid discs) are the same for: Cosworth 2wd, any Sierra (non-Cosworth) with rear discs, Granada mk3 (not estate or 24v)
Rear calipers (vented discs) are the same for: Cosworth 4x4, Escort Cosworth, Granada 24v, Granada estate, Scorpio 24v, Scorpio estate
There are 2 versions of the rear subframe, one for the 7" diff, the other for the 7.5" diff. Most regular Sierra's had the 7", all Granada mk3's (except the 4x4) had the 7.5".
Rear diffs
7" version - The Cosworth 4x4 and Escort Cosworth have the 7" diff with 3.62:1 ratio and LSD. The same diff is fitted to the 2.8 and 2.9 XR4x4 and the Granada mk 4x4.
7.5" version - The Cosworth 2wd has a 7.5" diff with 3.64:1 ratio and LSD with 108 mm drive flanges. The Granada 24v uses the same diff, but has 100 mm drive flanges (like all other Sierra/Granada diffs). 108 mm drive flanges can be swapped over
The fitment for prop shafts and driveshafts is the same for all diffs (except the Cosworth 2wd with the 108 mm flanges)
Rear suspension arms
All rear suspension arms for the Sapphire Cosworth (2wd and 4x4) and Escort Cosworth are the same. They use uniball joints to the rear subframe, unlike the rubber items for all other Sierra's. Granada 24v also has the uniball joints, but has different suspension arms (wider and more negative camber, but do fit with the correct driveshafts)
Rear shocks
All the same fitment for Sierra Cosworth/Sierra 4x4 and Escort Cosworth (Koni's are even same part number)
Front shocks
Cosworth 4x4, Sierra 4x4 is the same fitment (Koni's are even same part number)