Thanks for your response : ) Maybe I'm doing something wrong, but I've loaded the two .img files into separate volumes which i can now see in the BII desktop, but when I open them, they just appear as regular old .img files that won't open (cannot find a translation extension). Am I doing something ...

Thank you! Do you mean add them as two separate ones or one with both inside?

Been scratching my head all afternoon over this... I installed Basilisk II onto my old Macbook (I've been using Sheepsaver but documentation told me I need BII for this software I wish to use) and have a folder of the app in question which holds both "1 - Install.img" and "2 - Install...