Form fins? Knock them down with a diamond cup wheel in a 7” angle grinder. You will kill a 5” grinder and a 9” is too heavy to hump around a vertical wall. Get a LOT of tarps and have it wet sandblasted if you want a quality finish on it. Unless the paint has lead in it, in which case do nothing but encapsulate with a shellac-containing primer and paint. Do not grind or sand yourself if it contains lead.