The Minnow was designed back at a time where the airplanes were not very fast, and were heavy due to the crude radios available. My racing partner back in the 80's dug up a Minnow for another buddy to get his feet wet in F1, and while it flew, it was not all that great. The under-camber was something that was best left to WW1 aircraft and free flight models.
If you want to cut new cores, I would use the SD6060 section with no washout. Adding a bit more area also helps, especially if you are flying at altitude. Easy to do by adding a few more inches to the length of each core. Also do not delete all the dihedral. While the original kit design had quite a bit, some is necessary to prevent adverse roll with rudder input.