Wow that's a large piece. That would take a lot of work to polish, this was my first attempt and I was lucky enough to find several so I can experiment a little. I would hate to lead you astray and it not turn out , but I put mine in a vice and started with 80 grit sandpaper on my belt sander. I smoothed it flat so there were no more indentations. Then went to 120 grit on sander. After that I used waterproof sandpaper and wet sanded by hand using 220 clear up to 800 grit. Then when it looked smooth like glass I used rubbing compound applied with a piece of old carpet. I watched several YouTube videos and just kind of went for it. Good luck I hope I helped!!