According to Bochan M. Kim, the series is based on an ancient Chinese story about a monkey who (for all his sins) got trapped under a rock-mountain for 500 years until a priest freed him under the condition that the monkey would help him get to this place he was travelling to. It seems Sengoku was the name of the monkey, and Benten and Goggles were 'allies' that he met while travelling with the priest. Even the exploding necklace is based on that story... when the priest freed Sengoku, he knew that Sengoku was a criminal (he even did something bad in heaven!), so he decided to put a metallic ring around Sengoku's head. Whenever any of the three wouldn't listen to the priest's orders, he would cast a spell that would shrink the necklace, causing immense pain. The funny thing is, even the appearances match the old story - Sengoku was a monkey (!), Goggles was a pig (!!), and Benten was a goblin (!!!).
Viscera and Queen Ynci both also note that if you watch "Monkey" (which is also based on the above legend) you can spot the similarities between Monkey and Sengoku, Sandy and Benten, and Pigsy and Goggles :)
Viscera also says that there was once going to be an American live action Cyber City Oedo 808 movie!!! It was supposed to star Michael Madsen as Gogul, Nicholas Cage as Sengoku (!) and Boy George as Benten (!!) - but nothing's been heard for many years...