As stated it is not the same engine used in UK-market 6-cyl Series 3. It was developed from the Austin O-Series 4-cyl. The Series 3S has the Stage 1 flat front end and bonnet, but pretty sure it was still part-time 4WD. There was a petrol and diesel option, and were used by the SADF.
If you post some dimensions of clutch release I can compare to a spare I have - outside diameter at front and bore.
I also have a a used bush I can measure so need the bore of the hole in your flywheel and the diameter of the end of gear box shaft that goes in the hole.
Pretty certain it is the parts I listed to you on LR uk Net.