Filling a ding on a big block valve cover advice needed!

Try this.

Bolt the valve cover to a head that's not assembled. Take a torch with a rosebud tip and heat around the dent. Propane torch will also work. Don't get it red hot. As soon as it's heated up take a wet sponge and apply it to the area of the dent. The metal will shrink and possibly pop the dent out. Keep working it however let the VC cool between applications. I've waited as long as the next day before trying it again.

Make sure you have the VC bolted to a head. If not the heat may warp the VC