Success!
Completely removed all traces of SH3 including the save folder in my documents and downloaded another copy of the mod from discord here:
https://discord.com/channels/9071959...82655043706930
Turned off as much of Norton as possible and unzipped to the same drive I had it it before and followed the set-up instructions again and this time it worked!
I can only assume the first copy of the mod I downloaded (
not from OneAlex's discord) was corrupted.
Thanks again Kal_Maximus_U669 for taking the time to try and help, much appreciated.