J train terminal set up at 121 St after cut back from Queens Blvd in 1985

How did terminate at 121 St after Queens Blvd route was shut down. I read up on multiple sources that was single tracked operation and that the Manhattan Bound track was only platform used. The Jamaica bound track was unused until November 1987 when cross switches and ramps into Archer Tunnel was completed. Also i read that would switch over to center track after 111 St and then switch over to Manhattan bound track over Lefferts Blvd. What did the Switches look like at Leffetrs Blvd junction. And how was the operation going with the single tracked at 121 St?