I changed mine out with dacromatised bolts from Fastenal, Beneteau used 8.8 which is equivalent to SAE grade 5.
I upgraded to 10.9 which is equivalent to grade 8 and also added stainless steel plates with gussets to spread the loads. My bolts were M20 and the tensile strength is 30,000 lbs more than 8.8
In your instructions it tells you to thread the rod in to 37 foot lbs ,however it does not tell you what to torque the nut too. Hopefully its not stainless ,as stainless cannot be used in cast iron as galvanic reaction will cause the cast to eat away ,unless the stainless is coated to prevent this.