Ive followed what you have stated here and have had much better success, the model is much less deformed, but there is still something wrong with the bones. Viewing through Developer > Render Metadata > Joints. Sicne Im using the Avatar workbench model, I already have the properties set.
The mesh is deformed, but it only seems to be vertical deformation. From what I can tell via the Developer rendering options, the bones dont look linked properly, and seem to mostly be horizontal except a couple at the back.
Here is a screenshot of the model, left and center is SL, right is Bl