We hear about Old Man DiMeo a few times throughout the series, basically that he was the Boss of the family before Jackie Aprile took it over in 1995, that he was Boss from at least the '50s until his life imprisonment in '95.

Even though Jackie refers to himself as the "Acting Boss" for DiMeo, we never see him, or Junior or Tony confer with him, as the way Acting Bosses usually would with an official, de facto Boss.

And there's a lot of emphasis on Johnny and Junior and their role in the Family...It just makes me wonder if Old Man DiMeo was a front boss in some ways, a lightning rod...Or if he just gave Johnny and Junior a very long lease as Capos.

Tony says to Junior in the final episode, when visiting him in the asylum, that he and Johnny Boy ran North Jersey...

It just makes me wonder, given that DiMeo was seemingly cut out of the picture totally once put away, not really mentioned, and Tony's statement to Junior of how he and Johnny Boy ran North Jersey, it makes me wonder if he was just a front boss, at least until Johnny Boy died, at which point he was probably able to reassert control since no one liked Junior that much.....

I mean consider how it's mentioned that Tony and Johnny Sack were meeting and doing business with each other with regard to Barone Sanitation as far back as the early '80s...Tony was then only a Soldier working in his father's crew, and yet was doing business with the Underboss of NY on his father's behalf.

I think the way it was in the hypothetical world was that Dimeo ruled with an iron fist. So much so he didn't want to give up the title when he went away. I don't believe in the slightest he was the front boss. As far as the "running north jersey", I think it was like this. Although never explicitly mentioned in the show, the Sopranos I believe had a crew in South Jersey (mabye more). In saying they ran north jersey, I think it just meant that they were the most powerful crew in North Jersey under Dimeo.
I don't remember anything being said about Jonny Sack and Tone doing business in the 80's, however, if that is the case, I think its fair to assume Jonny wasn't number 2. Remember, Ang Garepe was said to be Carmine Sr's consiglieri before he went away on a "construction beef", in fact, Tony himself asserts that if it werent for his lengthy incarceration, he would have ended up taking over.

No, Dimeo was the Boss. As the series went on, he was no longer mentioned.

The producers left a lot to the imagination.