I did a bit of research on possible chainplate replacements, and came to the conclusion I'd have to make my own, which I haven't done yet.
But here is a sketch of the various options I looked at, including Wichard:
If you use the Wichards you'll have to re-drill new holes through the hull-deck joint, and through the aluminum reinforcing channel.
Steve Birch has some made up that look pretty good, too.
Peter
#1331 'Sin Tacha'