Alright, so I managed to get the weight slider working.

20 weight:

100 weight:

Now I just need to find out how.

The only thing I did differently was to use the normal UNPB body & skeleton, rather than the cleavage version.
For some reason, my _0 & _1 weights of the cleavage version are a different filesize, which may have been why my meshes were distorting.

The nodes are still out of whack though. I have no idea if that affects anything or not. More testing is in order...