Jamie McMurray remembers giving Kevin Harvick a quick rundown on go-karts. Nothing fancy, just the basics, the kind of conversation two NASCAR guys have in a parking lot. Six months later, Harvick showed up with a karting trailer that made McMurray’s jaw drop. “It was the nicest karting trailer I’ve ever seen in my life,” McMurray said. “A couple more zeros than three grand. Had two employees full-time.” That’s the moment McMurray realized somet…