Not me, but my father built some of the fastest flathead V8s in the southeast in the late 1940s and early 50s. The flathead was one of the most underrated engines in production, and it responded VERY well to modifications and race tuning. While the 223 Ford OHV six might have given a stock flathead a run for its money if the six was race tuned, they wouldn't have been able to stay on the same lap as a well built flathead. Now the Hudson flathead six- - - - -that was another story entirely! Those things could "shake the trees and rake the leaves"!
Jerry