The machine shop did an excellent, outstanding, amazing job of cloning the first 8 chainplates.
It took some beating to get the new ones into the boat. Mostly the beating was because the new steel was perfectly straight and the fiberglass knees are slightly irregular.
The trick appears to be this. Get a few bolts through, tighten them down good and hard. The slight flex will bring a few more holes into alignment. Eventually, all five bolts are tightened down hard.

The mainmast top spreaders are next. They're ⅜″ steel instead of ¼″. Once those are done, I can tighten down the mainmast because it will be all done.
I think I can do all six mizzen chainplates in one big batch. I can rig the two halyards forward. We have two backstays. That should do while we're on the hard.
As I write, we're not 100% totally, totally done. We still haven't put Life Caulk into the openings yet. That's tomorrow's chore. It doesn't take long. After putting 8 chainplates in and taking two more out, I was just too tired to face caulk.
Then it started raining.
So I scrambled around putting tape around each opening to minimize water intrusion.