Steve,
Take a look and see if maybe the trigger stirrup is being stopped in its rearward motion by the notch in the grip safety lever. Something has to be stopping it if you've backed all the way off on the overtravel stop and the halfcock still contacts the sear. OR, you have an out of dimension pin hole and the disconnector can't move far enough to clear the sear. OR, remove the topend and try lowering the hammer with the trigger held rearward. If it still contacts, it isn't the linkage or safety pins.
Keep at it Steve, you'll figure it out yet. There are only so many pieces in there
and you just have to isolate the offender. BTW, check the little piece that sticks out of the top, front of the top safety lever...the one that actually pushes up on the bottom of the plunger. Sometimes guys will bend it as they hold the pistol upside down while putting the slide back on the
frame. I don't know if it would function with that lever bent far enough to stop the trigger's rearward motion, but it's worth a look.
Let us know what you find.
Bob