Unless you live in the land of no train shows, why fool around with this stuff? You can buy old postwar O27 uncoupling tracks for $1 or so and harvest the electromagnets from them. Solder on some extension wires and install in your track (I use Gargraves). I have dozens and dozens of these on my layout. I just bought 6 of the tracks (for a total of $5) at a show yesterday for a friend of mine. You want the tracks without the postwar controllers, lots of times they are in under the table junk boxes.
Add a momentary pushbutton for control and uncouple away. The buttons labelled "U" are the uncouplers.
