I am trying to hook up a vacuum line from the manifold to power brake booster on my ford 1976 302 engine in my 1953 F100. Behind the carb there is a port that has a threaded plug. It is a find thread that will loosely screw into a 3/8 ntp fitting. I have been unable to find a fitting that will screw in to the port correctly. The manifold is stock Ford manifold # 08AE-9425-B. Does anyone know where to find the correct fitting?