tammelbelg - thanks, that did the trick.
Initially, I had the Blueprint and Environment folders (.uasset files) in the Content folder as below (which was resulting in errors):
NG:
Unreal Projects\FeudalJapan_Meshingun\Content\
I referred to file hierarchy of other existing projects in the Unreal Projects folder, and then moved the FeudalJapan files down one level below the Content folder as below.
OK:
Unreal Projects\FeudalJapan_Meshingun\Content\FeudalJapan_Meshingun\
>Blueprint and Environment folders are here.
Hopefully this helps anyone else attempting to install .uasset files manually.