I have a Greener Self-Acting SN 364xx. It is in minty shape, but not high grade. In the guns's case is a cocking tool. I was told the gun cannot go together if the hammers are dropped until they are recocked. Since you recock with the underlug hooks, they cannot get up under their spot to work when the hammers are down, hence the recocker tool. The little pieces that do all the work of ejecting and cocking have to be in the proper position when putting the barrels back on. Nothing fails into place automatically. Just line up the bits with the ejectors out and it will go together with just a little push to get the cocking hooks under the hammers. I don't let friends try. I show them if they are interested.
Really a flat head screw driver can do the same function. If you didn't know, you couldn't get the gun back together.
The tool has a curved notch that fits the hinge pin and a flat piece that goes up under each hammer.

Joe