In previous years of the NESKS, the Stock Motos and KZ/ICC shifters ran together, although scored separately.
This season however, the two classes in the series were split and ran at different times, for the first time. I loved the sight, and once actually being in, a grid of 30-40+ 125 shifters ready to blast off at the green. But at a few races this year, there were simply too many in both classes to squeeze into one race. (A wonderful problem to have though when you think about it).
Any Modified Moto karts, as opposed to Stock Moto, would have been put in the KZ class. But Mod Moto (Open Moto) karts in the series are a rare sight. The KZ class is usually completely KZ-powered.
Having said that, Open Moto karts have run there before, and if you showed up with an Open Moto kart at an NESKS race, I doubt they would turn you away. How they would score you, I don’t know. They might class your kart completely separate from the other classes, but they’d place you somewhere. Like Clark said above, the people who run the show are a good group of people.