I also have Giovanni Lombardo Radice (aka John Morghen) as a friend on Facebook, and he's been talking this movie up quite a bit. He seems to be involved with this one, but says that David Hess is not involved. A quote from GLR on Facebook:
Friends and fans, I got the official permission to announce that Ruggero Deodato and myself are working on the sequel of HOUSE ON THE EDGE OF THE PARK with North Bank Entertainment company in UK. We are very excited, but very sorry that, due to too many bullets through his body, David Hess can't be in it. But we hope he will approve of the project which will be somehow dedicated to him.
What this movie will be about, I have no clue. I've always wondered what would become of Johnny's character after the events of the first one.