I don’t think he would mind. I talked to him some time ago and arranged for the needed legal permissions to copy, share & modify. See the license file inside GitHub - i6/ibg: Inform Beginner's Guide
He had lost the original source material for the IBG and there was work to re-create it which now exists on GitHub.
You should be able to re-use things as long as you follow the license terms, which don’t have very many requirements.
The same is also true for The Cloak Of Darkness, which now exists at jxself.org public git repositories - cloak-of-darkness.git/summary
You should notice that the file cloak-of-darkness.inf has a similar permission to the IBG.
His permissions didn’t extend to just the IBG and Cloak Of Darkness but to all of his Inform material.
I had started working on converting things from his website but haven’t worked on it in some time:
jxself.org public git repositories - inform-resources.git/summary but hope any of this helps.