I'm contemplating using a set of ensign chainplates $21 each: http://www.ensignspars.com/parts
from the description they sound very close to the right size, Might have to re-drill the hole for the clevis pin from its' current 5/16" to 3/8"
I've traded a couple of emails with Zeke Durica at ensign spars.
His ensign chainplates are to use his description, "1"X 1/8" thick X 10" long. They are 5/ 16 hole on the top and 3 3/8"s holes at the bottom up 3/4 inch 2 3/4 and 4 3/4."
I haven't been near the boat yet to compare these dimensions.