Rusted barrel

Hey guys, I got this handmade grill for 50 bucks but this is the inside of it. I’ve gotten rid of the flaky rust and hit the majority of it with a wire brush. I bought a wire brush for my drill so I’ll go at it more tomorrow and clean up as much as I can. The pores are pretty deep and I don’t know how much I’ll be able to get out. How much of this do I really need to worry about for it to be safe to use and what’s the best way to clean it aside from a wire brush and a scuff pad? Made from 1/4 inch steel I believe.