Well there's no way it'll go between the shell latch and the receiver. First, the shell latch has an offset into a slot in the receiver and the release lever won't physically fit in there. Even if it did, it couldn't pivot up and down due to being trapped in the slot due to it's own offset where it overlaps the latch lever.
Second, pushing in on the latch button pivots the back end of the latch out into the loading port such that the release lever hits it and won't go into place. The only way the trigger group goes back in place is if the back end of the shell latch is retracted into the slot to clear the release lever. I tried to do it the other way and it just won't fit. The headed pin is also correctly installed-you can easily see the recess for the rim of the hollow pin.
The release lever is already being pushed up far enough that it hits the bottom stop on the housing, so it can't be lack of movement on the release lever.
HELP!!