There are many differences between a 14" and a 16".
Front uprights are different to allow larger diameter brake discs (280mm vs 258mm), the calipers and pads were the same as 14" or 2WD. Rear brakes are based around the LT (270 x 55mm) of the time so have larger diameter drums, bigger shoes and rear hubs to accept a larger backing plate.
The rear driveshafts, CV joints, gearbox flanges and hub-shaft flanges are larger and much stronger (108mm).
The front driveshafts were the same as a 14" when the 16" vehicle came without a front diff-lock but had larger diameter driveshafts and outer CV joints (98mm) when it was ordered with a front diff-lock.
The 16" was the only T3 Syncro to come with a rear diff-lock as standard. All other T3 Syncros had to pay extra for diff-locks. *
The rear trailing arms were 25mm longer to accept larger diameter tyres (195R16 or 205R16) and these came on 16" steel wheels that were 5.5" wide with ET34.
The gearbox and front diff used different final drive ratios. In a Syncro 14", the standard petrol ratio (other options were available) was 4.86:1 and a 4th gear of 0.85:1 was used. In the Syncro 16", the standard petrol ratio was 5.43:1 (other options were available) along with a 0.85:1 4th gear (note, this was not just a Syncro 14" TD gearbox as they use a 0.78:1 4th gear ratio). For the TD Syncro 16", it was usual for the 6.17:1 final drive to be used but with a 0.85:1 4th gear. 5.83:1 was also used but they were not as common. They were fundamentally the same inside, just with different ratios and larger output flanges.
The same springs were used on all T3 Syncros but the shock absorbers on the 16" used stiffer shock absorbers (stiffer rates both in bounce and rebound rates than the standard 14" units) - they are physically the same dimensions as any other factory T3 Syncro shock absorbers.
There were body modifications also.
Some words of knowledge by a crazy UK Syncro nutter on the topic of differences between 14" and 16" factory syncros:
The use of plastic/rubber arches were used to cover up where the back of the front and rear arches were cut to allow more space for the larger diameter tyres.
There were body strengthening plates placed inside on the rear 1/4 panels (fill-in panels), at the front (top and bottom) of the sliding door opening and also above the sliding door inside the roof (not visible). The last extra strengthening parts were placed around the front suspension mounts, inner and outer plates were welded onto the chassis rails and also over the top of the turret rear facing area.
There were officially 2138 Syncro 16" produced.