You MUST have the shoulder on the cock. That's what stops its forward travel. You don't want the tumbler taking this punishment.
1) On a new build, inlet your plate.
2) Then install the cock on the lock, with cock in lower position. Put a light coat of inlet black on the inside arm of the cock, and press the lock into the inlet as far as it will go. Pull it out, and you will see a black spot where the cock touches the wood.
3) Cut the wood away. repeat #2 and #3 until the lock plate seats completely.
4) Put cock to half cock position, and repeat #3 until the lock plate seats completely.
5) try the cock from lower to full, with inlet black on its inside arm. You will need to have a slot for the trigger so you can lower the cock. Pare off any spots that bind.
6) install lock screws and tighten up. Repeat #5. Pare off a whisker more than you need so the cock has freedom of movement when the wood swells up from humidity, etc.
I put inlet black on with an old toothbrush, hardly enough to see on the metal, but it shows on the wood.