Schuyler Have you tried using the Kadee #12 coupler? As of a couple of weeks ago Kadee has been selling the #58 couplers in a pack of 20 pair along with the flat centering springs.
I've been following the Sergent coupler comments and they sound nice, but I understand they have a better one coming out later. We have been hearing about the Barger couplers for a couple of years and still nothing in sight. I just wonder how many people will finish a car and put it aside until the perfect coupler gets produced. The more of the 58 I install the less likely I will change over to the perfect coupler if and when they arrive.