Yes, I thought you could use the native Linux partition tools and then dd(1) to copy over the GRUB partition from your current drive A.
What do you mean by “compare A and C”? You need to construct C as a copy of A as far as partitions are concerned.
If you suspect there might be something wrong, why not set a convenient maintenance window, export and save config, reinstall, import config?
The boot pool layout, GRUB and stuff are not part of the saved config. You will be getting a clean factory new boot pool and auxiliary partitions.
P.S. Just noticed the other thread.