Then I began to wonder why there's so much paranoia about a square exhaust port design. They are so worried about the ring expanding out into the exhaust port that they always recommend a roundish design. But consider this: the rings are trying even harder to push outward into the transfers than they are into the exhaust port. That is because the rings at the exhaust are basically the middle of the rings and the sides of the rings are located at the transfers. When you squeeze the rings shut when installing the piston/rings into the cylinder notice how it's the sides of the rings that move toward the center point, not the middle of the ring. So look at how wide the transfers are at their straight tops and by that you know how wide a straight center portion of the exhaust port can be.
So if you port for a target rpm and don't achieve it then consider squaring the exhaust port top little by little until you get the speed you want. But know that a rounded top preserves mid range power better than a square top.