Some of the best engines use pushrods, and custom buiders of both Harley's and automotive V-8's use 'em. I can't tell you how much technology there is available for this kind of application. If you want to build the best custom Harley in the world, you're probably going to use an engine with pushrods. It will be really cool and provide stomping power. It will turn every head. You can solve every technical hurdle so that you exploit the strengths of the engine while reducing its weaknesses. But that doesn't mean overhead cams are inferior by design. It's the specific implementation that's great.