Thanks for all tips, I think I start from rear discs as they are badly corroded and should be changed anyway due to MOT in Nov. -21. My prop shaft was off some years ago due to change of rear crank seal. I believe it is correctly fitted but could you explain how it should be; three bolts in gear and diff. If one of the three in diff side point down should one of the three point down also in hear side or what this fig is showing to me. Explanation needed please.
OK, typed here is same for diff and gear sides, but focus on diff:
Connect donut to diff, and as the photo shows bolts go into donut and diff entering towards rear of car (so nuts come from back). As you hold the rubber donut, identify the three 2-hole pairs (thicker area for each), and have one pair point towards the floor/road. Put a bolt through the LEFT hole and into the diff, secure loosly for now with a nut. I assume the car is rear jacked or in a lift. Rotate the rear wheels and again do the LEFT hole to diff for the other two 2-hole pairs. As you look at the donut, prop bolts always go to the RIGHT hole when the thick donut area point downwards. Not that with the prop to donut mating the bolts enter behind the donut so the nuts in the prop connection are holding the prop (study the photo closely).
I installed my prop on and off many times, always with the car lifted (not jacks). This way gear was in Neutral plus the rear would spin by hand (easier than try to rotate the diff by hand). Also, it was impossible to insert the donut-to-prop bolts from the rear unless you find that sweet spot where it is possible, I would say when you face the donut, it is in its 4 o'clock position IIRC. To tighten I use a spanner to holt bolt/nut behind the donut and in front I used 1/2" air impact wrench with 2 long extensions to get a down angle if exhaust is intact (and often a friend on the spanner).
Lastly, try use paint or white correction fluid to mark 3 lines on one of the prop to donut mating and two lines for diff to donut, for future reference.