I modified the bolt retract arm by adding a "shear/latch" to the front end of the arm in addition to the latch as shown below:

This engages a slot that I machined into the "ratchet" rail as shown next:

When the handle is pulled back opening the bolt the arm drops into the slot and keeps the bolt retracted.


When you want to close the bolt you simply push the handle forward and the bolt closes.
If you look at the latch you will see that it is lifted when you pull or push on the handle, thereby pulling the "shear/latch" out of the slot when the handle is pushed forward. The main issue I see at this time is that the ratchet rail has a cut in it for the bolt rail rivet which removes some of the locking surface for the arm to lock into.