Radar, 80% eff. is pretty high for this type of engine, 70 would be as high I would go. The calculator assume the information is 100% accurate and you never plan to vary from it. Change some of the parameters around, one group higher and one group lower then average out the sizes. Vary the eff and rpm and even the timing a degree or two. Did you degree in the cam when it was installed? if not, then just going off the cam card will give false information, again vary the inputs and average.
When going from port size to pipe size, be sure to blend them in gradually. If welding pipes to pipe, always have the inserted pipe going with the flow. Avoid any edges inside the pipe that will catch the flow of exhaust. When you get to the collector, pull the two pipes together forming a flat (think of two letter D's laid flat to flat) with a oval collector over them.
Good luck and let us know what you do. Joe
