The Sicilian born in Castellammare (the town of Maranzano & Bonanno).

Is he, or is he not, the underboss of the Gambinos? Or perhaps he was momentarily?

No...
I heard Maninno is the UB
I don't think palmeri have anything to do with the gambinos anymore.

Sicilian? A person associated with the “zip” faction?

He's in an Italian prison. In the extortion case he relied on a group of criminals from Campania, who had connections to NY, through their leader who had been living in Brooklyn for years.

Not, nor ever been in administration position. He was one of Giovanni Gambino most trusted guys, who belonged to the zip crew. Ties to the Anello, Asaro, and Bonventre families of the Bonanno family, and surprised he did not join up with the Bonanno family. He received a 20 year sentence and is in his 60's, so when he gets out of Italy prison, he will most likely retire and move back to Castellammare. That is what Meyer is saying about not having anything to do with the Gambino crime family anymore.

OK, well it’s claimed he is or was the #2 in some capacity on Wikipedia. Another thing I’m trying to ascertain here, maybe, is the Sicilian influence now bigger than ever in the Gambino administration? Or at least in a long time.

‏ it's certainly bigger ever since carlo gambino days
Because after big paul gotti (who from naples) was in charge
So yeah it's the biggest since carlo days

Who is the boss then? Could this alleged internal dispute and demotion of Cali be a scheme to throw off law enforcement?

Well maybe so
But as far as i know cefalu is the boss
But great point you have here, who knows maybe it's cali ( for the sake of the gambino's i hope it's cali) because i think that he can lead them to a great future

Could be they're taking a page from the Genovese playbook, is what's goin on.

As one of them as street boss ?
I bet it would be cali
And if it's true i'm sure he probably came up with the idea
Cali is considered ad very smart mobster

Well for some years wasn’t the FBI not 100% able to determine who the real Genovese boss was? That’s what I mean... tactics to evade prosecution.

Maybe so
Only time can tell
Or some source here will confirm