That's not an oil crossover, it's the breather system. The basic premise is on a extended-high-rpm car there may be too much crankcase pressure even with the usual means of addressing it. That combination of tubes and the higher breathers means it doesnt have oil vapor and eventually oil all over the engine compartment like a car with the breathers right in the valve cover might. It gives the vapor a chance to condense out of the crankcase gasses and run back to the valve covers. Usually you see them on circle track and road race/Trans-Am type engines.