@anewday apologies for my perceived lack of patience
@mistwang thank you again; figured it out from what you said:
Go to the conf folder of your litespeed installation directory e.g.
And edit the mime.properties file and append:
shtml = application/x-httpd-shtml
Obviously you may still need to update your virtual host template to include index.shtml files as an index file (from the web admin go to virtual host templates, edit, general, scroll down to 'index files' and edit the 'index files' list).
Hopefully that's helpful to someone else (or me later)