drive failing, dd back failed at 33%, can I partially recover?
Anyhow, it failed around a 1/3rd of the way through. And now I have a partial replica of about 350 GB.
Your chances from a partial replica are very slim. Data in a file may have pieces in the good part and pieces in the failed part.
A local recovery agency is likely your best choice.
Second choice might be Recuva (cc cleaner) or Spinrite (https://www.grc.com/sr/spinrite.htm)
There are other tools and methods such as ddrescue, but none are guaranteed to be completely successful.
DDRescue
If the tools do not recovery data then it is gone. Not much else you can do.