some people (CoastVW for example) will tell you that it is possible to change the input shaft on a difflock syncro without moving the diff aside; evidence of my eyes and hands is that it is very very difficult to do successfully and getting it wrong can result in the input shaft rubbing against the end of the crank and pushing the complete input shaft forward, thereby loading the mainshaft bearing more than it already is; in that event it may also possibly lead to excess wear on the dog teeth of 4th gear and the synchroniser slider resulting in the gear starting to pop out of gear with concurrent damage to both.
So yes move the diff aside;
You need to remove the flanges and adjusting ring covers and then the adjusting rings. A strong thing tipped 3mm screwdriver will allow you to prise the flange caps out, but if you want to be brutal with them then you can just fit new ones afterwards.
Before removing the adjusting rings you need to accurately mark their position relative to the case and ensure that you know which one is which side so that you can ensure that when put back in the preload on the differential bearings is maintained and the backlash set up between the crown and pinion is also maintained.
You can make a tool to enable you to turn the adjusting rings using a short length of 60mm tube and some way of driving it, like a tommy bar, something like this
60mm tube, you may need to use a grinder on the outer edges to ensure a nice fit in the multifaceted adjusting rings, you shouldn't need more than 300mm of tommy bar to enable you to undo the rings and do them up again. The rings are lubricated when fitted with gear oil, the o rings are well oiled too. Once fitted wipe off any exuded lube.
You should replace the circlips (014 311 317) for the output flanges every time as they are stretched a little and pressed into place when fitted and you will stretch them again getting them off as there is a belville washer underneath them maintaining pressure on the flange holding them against the shaft of the differential. The best pliers I have found for removing and fitting these snap-ring circlips are these
US Pro and they are cheap
use them one way (broad side) for removing the clips, the tips work best for reseating ime
When refitting the flanges you may need to push them down their splines once started, a 32mm hex socket (or tube of a i.d just bigger than shaft of diff) will allow you to drift them down the splines to the stop, and same for fitting the circlip, remember the belville washer, convex side up up, open up the circlip just enough to seat on the end of the shaft and then tw4t it into final position with the 32mm socket and double check circlip is fully seated in the groove. If you pop a pin down the edge of the flange cap as you push it into place you'll allow out any air under compression and then you can withdraw the pin, I use a medium safety pin.
Re the input shaft, once you can move the diff aside a little to ensure good access to the circlip and to allow you to reach in with something like a strong magnet or something (I use my Grandad's special home-made Meccano spanner, made for building a big Eifel Tower model
)_that will allow you to pull the sleeve towards you until you can unscrew the input shaft.
There is a double ended 7mm threaded joiner and this should be screwed fully into either the mainshaft in the box or the new input shaft (I prefer to screw it into the mainshaft, before I put the diff into the case), new circlip N 012 419 1 on the input shaft then the sleeve and offer it up to the grub screw and screw it all the way on, then back off 1 spline, and slide the sleeve fully home and seat the circlip in the groove and double check it. The input shaft should have a little bit of a wobble on, not be rigid, very important, it is only fully supported when fitted to the engine and the spigot bearing in the crank is supporting the outer end.
Then it's just a case of putting back everything you removed and checking that you have a dadge of backlash at the crown wheel just as it was before you disturbed anything. So have a feel of it before you remove the adjusting rings.
Difflock diff it's best (maybe not totally essential, tbh I have never had to try without doing so) to remove the fork of the difflock, and if oil plates are fitted then space is a little more compromised than if they aren't but you shouldn't need to disturb the plate above the diff but be aware it's grp and the diff with crown wheel weighs best part of 10kg and is solid steel so be careful. I'd advise having a few clean rags about so you can use them as wedges to support the diff a little while your hands are busy with circlips and the like.
It is possible (with a bit of care and cunning) to effectively replace the input shaft without disturbing the diff on a 2wd or a non-locker Syncro with a 2 pinion diff, but it is difficult to do it on a 4 pinion 2wd diff as used in the 2.1 boxes like the AAP, which is why you see so many old petrol boxes converted to diesel and the 11mm cut of the end of the shaft insitu rather than go through all this.
It took me longer to write this post than it would take me to just do the job here with the correct tools.