Your problem is that the bulkheads in your G-26 are original. The bulkheads must be replaced with new 3/4" marine ply bulkheads (mahogany finish both sides looks best), then you mount your chainplates back in place. There is an article about doing this very project on this site - index
Use your old bulkheads as templates for the new.
You cannot use metal plates as you suggest on a G-26. You will rip the topsides up to the deck if you try.
Good luck with her.
By the way, a well maintained G-26 in our area goes from $12,000 to $16,000.
They are excellent sailing vessels - very fast and strong.