The driver's rail was definitely seated incorrectly, and that leak is gone now. Similar to a problem someone posted in the 300 degree forum, I couldn't get the driver's side rail to seat properly with the rails connected. I had to disconnect them, seat them and bolt them in, then reconnect the SS line that links each side.
I still have a very large leak from somewhere on the driver's side though. My boost leak test only holds about 3.5psi and rapidly loses pressure. Gonna have to look harder tomorrow when the sun's out. I just hope I don't have to pull the plenum again.