Metal working question...

[Irving]

So is a flap disc something I put on the angle grinder or does it go on another kind of tool?

Flap disk will work with a grinder. But I would use it for the final finishing after chiseling off the side plate.

Yes to both.

This is a flap disc. You've seen them before. They are more expensive than a grinder wheel, and don't last as long, but they take off material at a slower rate and leave a way better finish. These work great for removing paint and milscale and stuff.