Hi there,
I did this exact same job on my '82 300D/4.3 a couple weeks ago, and it is a very straightforward process. The only thing I had trouble with was that I could NOT remove the fill plug no matter what I did! I eventually removed the cover, drilled and tapped another hole for a 1/4" pipe plug and used that one to fill the differential. On my vehicle, the outer axle and inner axle shafts came out easily after lowering the differential and positioning it to the other side of the car as far as it would go. The inner shaft actually came out easier than the outer shaft, as it was very well lubed, while the outer shaft splines were a bit dry. I had access to a car lift and transmission jack, which greatly simplified the job. The same boot was split on my car, all the other ones looked fine.

Regards,
Richard Wooldridge
'82 300D/4.3L Astro V6 engine & Trans.