I agree with JRP's inclination towards the Bruce, if you really think you'll run into some rocks as you mentioned. We have the Rocna, and really love it here on the Chesapeake. But it's more expensive, and not very easy to stow without a bow roller. That's probably true of Delta, Bruce, and plow anchors as well, but they don't have the "roll-bar", which I think makes stowage that much more difficult. For us, the Rocna is not a problem because we have the roller.
As a kid, my family had an O'Day 28. We also had two Danforths, but then added a large Bruce, which we kept in the cockpit locker (no bow roller either). It was a good anchor. Since anchor choices tend to be such a hot topic, my recommendation is really my gut instinct--that the Bruce would be a good choice if rocks are a concern, and a nice balance with the Danforths.
As for rode, I second the comments that you need two sets of chain/rope. Perhaps the existing can me made the secondary, then a new set would be primary. I would also recommend 25 - 30' chain and 200 feet of rope. Perhaps 1/4" chain and 1/2" rope. With your 120' now, you're limited in depths and conditions in which you can anchor.
I'm no anchor engineer, so this is just what I would do if I had a similar boat/set-up. Of course, I'd probably look to see if I could get a bow roller installed so I could put a Rocna on the bow, but now I'm getting dreamy.
Good luck with your trip!