"Mr. Neil" got some coverage in "Boss of Bosses" and "Murder Machine," but as you and DC observed, he really hasn't gotten the attention a figure of his stature deserves. Perhaps it's because he spent five critical years in prison on a tax rap, which probably caused Gambino to pass him over in favor of Castellano (the fact that Castellano was his cousin and brother in law didn't hurt Big Paul either). Maybe, too, it's because he was ill with brain cancer for quite a while. About all you get in most books was that he was Gotti's mentor and protector.