Yikes... it's been many years since I did this upgrade. I can't remember the exact sizes required.
The best thing would be to measure the diameter of the posts on the alternator (and/or the distribution block on your car) and get ring terminals which have a slightly larger ID.
For the junction block, it depends on the setup for your particular chassis; as some chassis use different junction blocks. I've never owned a W126 so I'm not sure what those are like. I assume you have seen the "4ga" cable photos on my website in
this directory? There are some good photos of the W124 setup, maybe see if the W126 is similar?
