For some reason google wouldn't let me respond to David post.
The original aluminum chainplates were 1/4" thick. Enough of those
failed in the early years on the bay that most of the fleet was
converted to stainless. At least one prominent local rigger was using
1/8 stainless in the swap (with apparently no reported failure after
the swap.) There was also at least someone out there using 1/4"
stainless in the swap, because that's what my boat ended up with.
You're right, I should ask Schock what size and grade the new
chainplates are.

joe