Italian Citizenship by Descent?

Has anyone gone through the process of gaining Italian citizenship through their ancestors? We recently found out that my dad is eligible for Italian citizenship because when his mother was born (first gen born in US), his Italian grandfather hadn't naturalized yet and was therefore still an Italian citizen. My understanding is that as long as the birth occurred before the naturalization, my dad can get Italian citizenship. But I'm just wondering how difficult the process is, I know there's a lot of documents we have to collect - I'm trying to find out where I get a copy of my great grandfather's naturalization papers from 1942 because I know that's one of them. The index says it was processed at the Philadelphia court and gives me the file number and petition number. I know there's naturalization records at the Philly City Archives but they don't run as late as 1942. Do I just get copies from the Philadelphia Court House?

Also, what happens if my great grandfather had no birth certificate? I've noticed on the lists of documents needed it says Italian birth certificate but I don't think they were issuing them at the time he was born.

Thanks in advance.