GA Boater, Yes. It is a Riviera. My boat has stern mount plates, so I think i will have a pipe welded to a plate that can be bolted to the existing mount. Well, that's my plan at least.That is an oldie. Is there a name on it?
All I can suggest is a pipe slightly larger than the post along with hardware to secure the pipe. The problem is it might only be good to troll off the stern unless the downrigger can be locked to troll from the side of the boat.