Why did the surveyor ask to have them pulled? That is most unusual, unless he detects a fault or a condition that makes a fault very likely. Are these ALL the chainplates or just the shrouds?
More info would definately be a good.
Okay, with my "I make Satinless hardware" hat on I can tell you that testing your chainplates properly is going to cost more then replacing them is likely to. In the end the best test is unfortunately a stress destruction test....that is sort of a one way trip. And when dealing with old parts, you test EVERY part and not just a sampling as you do with new ones.
X-ray bombing the chainplates for cracks will not give you a true picture of whether they are ready to fail or not, it will just eliminate or confirm one possible cause. Bad odds.
Dip and paint tests that allow chemicals to interact with the surface and reveal things are even less reliable then x rays...but they are way cheaper and easier and if there is a major issue, it will surely show up...if there is a medium issue or a collection of minor issues waiting to domino, you're out of luck.
(Isn't it comforting to hear this info from someone that used to weld and test 300atmosphere pressure vessels the size of an office building and radioactive containment systems?)
I have no idea why your surveyor wanted you to drop the rig and rip off all the chainplates, but having done it...go to the extra expense of fitting all new ones, with the right bolts, backing plates and everything. check for hull deformation and abrasion/collapse in the areas that were covered by the chainplates, It will cost you a few hundred dollars all up...it will buy you 40+ years of peace of mind regarding that particular thing going wrong...and it will maybe stop some of those annoying mystery leaks through the deck, too.
In truth, though...99% of the time when something in the area of a chainplate fails, it is the terminal, pin or swage plugged into the chainplate, and not the plate itself. Cheerful thought, no?
Best of luck and congrats on your new purchase. I am sure you will enjoy your time on the water with your own boat immensely.