Unless you have access to the detail drawings that Ericson provided to the welding shop over three decades ago, and the chance of that paperwork surviving is slim and none, you are going to have to start over.
Having said that, I have seen local fabricators build bow and stern rails from a basic dimension drawing, and then take the tubing down to the boat and set it on the deck (use some protective cardboard) and measure the angle for the round feet. Some bring a small welder with them and tack-weld the parts and then head back to the shop for the rest of the welding and polishing.
Note that they will need not only the angle athwartship for the crown of the deck for the feet, but also the fore-n-aft angle resulting from the shear line for the top rail. Otherwise the top rail will not look right compared to the deck shear line.
IMHO: Good SS fabricators are both
artisans and
engineers, with or without formal education and certificates... :nerd:
Having watched some at work, I was mightily impressed by the craftsmanship on display.
Side Bar-- as to how Ericson and other production builders cope with this -- I know of one builder in the Seattle area that once provided a molded-out piece of the deck of his most popular sailboat design to his dodger and canvas company so that their product would be a perfect fit on that model, hundreds of boats down the road! I'll bet he did the same thing for the railing fab company also.
Good luck on your project,
LB