Use the chart in the book to match CSA with displacement. That is about as good as you can do without spending the money to buy a simulation package. If you want to get into the subject a little deeper then pick up a copy of PipeMax.

You can't really do much better than the simple chart that I put in my book unless you know some specific data on your heads. You would need to have a velocity probe to know if your heads have any dead area. If you don't know that type of information you just have to assume that CSA is CSA and so then you use the chart to see where the torque peak will be.

In the simple view the only thing you care about is CSA and displacement. A more advanced simulation will take a look at stroke vs. bore since a larger bore will provide some extra beathing capability. You need PipeMax to look at that. Rod length doesn't matter much but PipeMax will take it into account.