Glassed in and leaking chainplates make for a bad combination. Your wise to do something about it. Stainless steel
exposed to water
and oxygen deprived will be in less then optimal condition. If the chainplates were mirror polishe when new then they may be ok now. If not, then the surface holds the water
in the imperfections, creating pitting and cracking.
The other consideration in relocating the chaiplate inboard is that it will increase the load on that shroud
. Measure the length of the spreader and compare it to the "half-mast" measurement (centerline at mast
to chainplate). Supporting a vertical column (mast) with another (shroud) that is parallel to it is high load.
If the move inboard is smallish and your turnbuckle/wire will work, be sure to inspect them carefully; or if they're old maybe replace them.