Maybe use flat SS bar but try to prebend/twist the above deck portion to better align with the angle of the aft shroud?
Or, alternatively, use the flat bar but have your machineshop/welder fabricate a piece to weld to the top of it that provides the angles, as well as greater surface area for sealant.
My welder is only a hypothetical
welder at this point, but that is a possibility.
Approximate angles on the lower shrouds are 9 degrees inward (more than covered by the bulkhead angle) and 6 degrees fore&aft. which we will probably obtain thru a bend in the chainplate. An eyebolt, of course, would have no trouble with that much offset -- just aim it toward the mast.
I'm thinking we would start the bend below decks & angle the slot thru the deck, to minimize stress concentration of a bend at deck level. Dunno?
Nice thing is we can get 36" lengths of 316SS for, like, $17 each.
Polish them pretty. If Greg/Stumble wants to woo me with titanium, I'm listening.
Cuz one downside to the flat bar vs. eye bolts is ease of pulling for inspection every five-ten years.
Relative strength of materials (all 316 or 316L stainless):
1/4" wire: 1,400#WLL; 7000#BL
3/8" clevis pin: 2,400#WLL; 7,700#BL
3/16x1.25" bar (with 3/8" pin allowance): 4,100#WLL; 11,000#BL
1/2" eyebolt: 2,150#WLL; ~9,000#BL (per Suncor)
Since the Ballad originally had 6mm wire, either chainplate solution is likely to be stronger than the wire, which is prolly 2x overkill for the loads. It's not that big of a boat.
So it's down to convenience, fabrication cost, and durability going forward.