It's possible to dislodge a spider gear while sliding the pivot pin into place- - - -usually the one opposite the pivot shaft lock pin hole. One of my students at the Tennessee state trade school where I was teaching did that, and also locked things up on a test drive. A rear end will work (for a short time) with only one spider gear in place.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!