If the rail looks decent you can reuse it. I found on my 327 that I had to take a sharp heavy bar and beat on the rust boils to break them off. Once they're clean you can see what you're dealing with... I think there was a joint in the metal there on mine and I had to grind that down some to get the rail laying flat but it's not a big deal. Even if there was a small hole there I wouldn't worry too much about it. Get the rail flat. The hole can be filled with brass or something like JBweld.