I aggree that there are more modern parts. However a real J is a pretty good piece. Maybe not strength wise,but pretty efficient. I had a B&M and a Turbo Action. They ran nearly the same. The Turbo Action was a liitle looser. They did not look alike. The one pictured here looks more like a B&M. Mine were about 5-6 percent. I tried other converters,none were quicker. My friend worked on the J project at Chysler. He said that there was a lot of Dyno time developing that conveter. Way more than any probably spent today. I agree, converters can be a black art. I've had some from some name guys that wern't very good. At the same time those same builders did a great job for buddys combos. Try it in the car and test it.
Doug