Timing curve for my big-cam 451?

It seems you are doing this in the wrong order. Forget about the centri curve in the dist. Get the idle timing sorted out FIRST. I have a post in the Ign system about how to do that.
Once you have the idle timing sorted, you will know what your idle rpm will be. It may be lower with more idle timing because the engine is making more hp from the extra timing. If I read it right, your idle was faster with 39* at idle. Exactly what I mean. Because of the extra hp, engine may be happy to idle at a lower rpm. Whatever the final idle rpm is, you need to sort that first. Once you do this, you can look at the centri curve.