When you take your block in to have this done, the machinest will pretty much tell you what you will need to have done to it. Boring is just that, you are boring out the cylinders to cut away any grooves or imperfections in the cylinder walls. Honing puts a cross-hatched rough surface on the cylinder walls to help the piston rings break in (kinda like you scuff a surface before you paint it to help it adhere). Decking is where the top side of the block is shaved down because it levels the surface back out plus gives a perfect surface for a new set of head gaskets to seal to.
Since 400 blocks don't come in 4bolt, they only came from the factory with 2bolt mains, I would buy a set of aftermarket 400 splayed 4bolt mains and then when you have your machinest do yor work they can also drill and tap the holes for the splayed main caps.