Seriously, it's his interface that he created. Not to get his permission is definitely a no no and goes against the spirit of things. You need to get his permission imo.
He can choose not to respond at all and it'd be his right. I'm sure having his old site there generates quite a lot of traffic.
You may want to consider a separate domain name rather than something so long (something easier to remember).
Also, elsix suffered from people knowing about it. Which would be the same issue your website would have.
While it does have the benefit of a simple interface, I'm sure the old issues that killefiz had would come about (spammed entries) which took up a lot of his time.
That's something that elsix addressed.
Please make a concerted effort to contact him.