I would share the news. It might be deeply gratifying to the original creator that something has been remembered and found inspiring. There is really no potential downside because the original creator cannot stop you. It makes little difference if you do it now or when your comic launches.
It isn't the standard here on Tapas, but a few of us do use public domain characters. I've used characters from classic literature in my stories. A couple of guys here have done amazing things with golden age comic book superheroes. I had a thread going a couple of years back about Tapas series eith public domain characters, but almost nobody was doing that at the time.
Out of curiosity, how did the original creator specify that the story or character was being gifted to the public domain? There are a few different ways of doing this. Personally, I release stories with a Creative Common license. CC is not technically the same thing as public domain, but effectively it's the same thing. This way, the terms of exactly what can or cannot be done with them are spelled out and no confusion should result.
