5/16" is probably overkill as it is 2 1/2 times as thick as what was there. I would use the same thickness that was there originally. It did last 38 years! Type 316 is the best choice - 2205 is best used for its design purpose, pipes and tubes. And you want bar stock, not plate cut to size.
The key to their longevity is keeping them dry where oxygen is not present. Your deck must be cored and it is no doubt wet or there would have been little or no corrosion. I'd look at the core as well.
As well, you are probably compromising the rigging strength by using nicropress over a good machine swage I think.
I don't know where you could find any locally because I do not know where you are.
Living aboard in Victoria Harbour
Last edited by mitiempo; 08-06-2010 at 10:35 PM.