Exhaust port porting?

I have been sick the past couple of days so I have had time to day dream on my build. I have a question:
I am going with a 2.375" primary tube on my sc build and was looking at how to fit those pipes. My plan is to not make adapters but to make my own flanges. That being said I have not touched the heads with the prior roof issue and was planning to keep the same square shape. Can I make the head port opening more of a D shape? has anyone ever done this?