I’m actually using the Texture of the blockSolid Prefix depending on the Material that the Anvil is made out of. Most things that can be placed ontop of the Anvil will have their blockSolid Texture used too, except for Gems which will use the blockGem Texture instead.
And the NEI Icon is a separate Texture that I use in a lot of things.
But in the end its just a bunch of Block Bounds being Rendered, kinda like for Stairs or Fences or the actual vanilla Anvil.