Brendan, my '50, 216 fitting is the original one and is simply a cast brass 90° 1/8npt to 1/4tube, smooth hose barb fitting. A 7/16 wrench fits it just perfect. All I can think of is the restorers friend, "Kroil it", when its warm and if it snaps of just drill it out with an 'R' tap drill and clean out the threads with a 1/8-27 pipe tap. Coat the drill and tap with grease to hold the chips so they don't fall into the manifold.
Denny Graham
Sandwich, IL
