If I might throw in a few comments on this subject. First, adding a 350 pounds to the foot of the keel makes sense but the additional weight aloft due to the heavier wire (and possibly a radar dome) will cancel out any stability benefits the extra weight might offer. I am also concerned that the boat's stability will be further compromised by the weight of all the gear and supplies stowed in the cabin. Since space is at a premium, the boat's center of gravity is certain to rise.
I also believe that these boats are already overbuilt. Compare them to other boats that have made such voyages. Also, when was the last time one of us lost their mast? If I am sailing in conditions where my mast in in serious jeporady then I expect to have a great number of other more pressing problems, such as waves, and staying on board, and being wet and cold.
So far we do not know if we are travelling alone or with a companion. My preference is the latter of course but this exacerbates the challenge as you will read below. Basically, work out your personal needs and then multiply by at least two.
Now here is the real problem with these boats. Day-to-day living. Next time you go sailing, set the boat on a beat, healed over to 25 degrees or so, and then spend an hour below making lunch. Try dressing. Try Sleeping. Will you sleep in the V-Berth or in one of the quarter berths? Which one? Then try reading a chart. Where will you keep your charts? How about today's chart? And what happens when you open that ice box to retrieve your rum bottle? Where will the chart go? When heeled 25 degrees it will be on the cabin floor for certain, as will everything else. And because there are no good options for what to do with foul weather gear (remember we are paying a visit to Cape Horn) all below will not only be chaos but will be wet too.
Next, what about supplies? Food and water? Clothes (remember that we will pass from the tropics to the sub-arctic and back)? Sails and miscellaneous gear? These boats are tolerable for a week's cruising but one would have to give a lot more thought to stowage before heading off on such a long voyage.
Watermaker? Probably a good idea. But powering this and the rest of our toys will be part of another post on this subject. What about cold? A diesel fired furnace such as Espar's would be a great thing but adds both complexity and cost to our boat. (Aside: it is a pity that I cannot think of a good place to install a small stove such as a Force 10 as these are much less expensive! Sigh.)
Basic priorities then: safety (meaning keep the boat afloat and ourselves on board), then protection from the elements (read warm and dry), closely followed by food and drink (assuming one can keep anything down). I believe that the boats are quite capable of making this trip as presented (although I do like the idea of a water-tight lower hatch board). The question that I would like to propose is what changes are necessary to ensure that WE can make the trip?