I used a spezial lock ring tool for that.
After removing the rear driveshaft and yoke you have to remove a seal and a lock ring at the end of the rear housing where the speedo gear is installed. Itīs a bit tricky to remove this lock ring because there isnīt much room beside it.
You also have to remove the front driveshaft and pinion yoke because you have to pull out this shaft later.
While removing the rear TC case take care of the oil pump thatīs on the right shaft and itīs hose that ends in the left of the TC. Thereīs also a little magnet at the left bottom of the TC.
On the pic belos the oil pump is blue, the hose is red and the magnet is green.
When you removed the rear housing it looks like that.
Then you pull out both shafts incl. the chain.
After installing all gears from the old to the now shaft you have to put in the two shafts and the chain. Then you only have to reassemble everything (incl. the new rear housing for the speedo gear).