What exactly would you like to do?
(You can’t add vanilla items to these, without redoing vanilla items and overriding engrams and loot caches/dino drops)
If you want an anvil to make “new” items all you need to do is;
Duplicate all workbench files (core,engram,inventory,structure)
Link all new files and empty the default inventory items and default engrams
Create new items you want to craft in it, add them to the default inventory, and add an extra default engram (set it to 1 if you want them to need the engram)
On those new items, set their default inventory requirement to your new anvil. (I named mine the Super FABricator cause it was not playing well with others)
^ This makes it so the engram knows where to be made, and the item knows where to be repaired
Add the new Anvil to the structure placement list, add it to the master item list, and additional engrams and spawn one in the editor, place it down, and use giveengrams (so you learn everything) If you put in your custom items in the engrams, then they will appear in the anvil.
*Edit - I have a mod on the workshop with a custom mortar and pestle, custom anvil and custom fabricator for my new items i’ve added in, and don’t want to break the core reality of existence every time they add new crafted items ¬.¬