No. Naruto has its own unique world, lore, and characters. While the Avengers are great in their own right, mashing them up in a fanfiction might not resonate with the majority of Naruto fans. They are used to the ninja world, the chakra system, and the specific relationships in Naruto. The two concepts are quite different in nature, so it may not be a widely popular idea.
In a 'naruto is an avenger fanfiction' plot, Naruto could be brought to the Avengers' world because of a strange rift in the multiverse. There, he meets Captain America and is intrigued by his sense of justice. Naruto joins the Avengers in their fight against Loki, who is trying to use Naruto's chakra for his own evil plans. Naruto has to adapt to this new world while also showing the Avengers the power of friendship and determination, which are key elements in his own story.
One idea could be a crossover where Naruto gains Saiyan powers and teams up with the Avengers. He could use his newfound Saiyan strength and speed, combined with his ninja skills, to take on powerful villains. For example, against Thanos, Naruto could use his Rasengan enhanced with Saiyan ki energy.
It could be Captain America. He has a strong sense of justice and kindness. So, if he found a dog, he would surely take it under his wing and protect it. Maybe he'd even train the dog to be a mascot for the Avengers.
In some fanfictions, the 7th Avenger could be a time - traveler from the future. This person has come back to prevent a major disaster that the Avengers couldn't handle without their help. They know all about the future events and use this knowledge to guide the team, but also have to be careful not to change the timeline too much.
Percy could also be a big fan of Hulk. Just like Percy has his own 'inner beast' that he sometimes has to control (his demigod powers), Hulk has his own anger issues. Percy might see a bit of himself in Hulk and also be in awe of Hulk's raw strength. He would probably be interested in seeing if there's a way to help Hulk better control his rage, using his own experiences of self - control.
There have been many suspects over the years. One theory pointed to a person with a connection to the seedy underbelly of Hollywood at that time. This person might have been involved in illegal activities and had a disturbed mind. But without conclusive evidence, it's all speculation. The case is complex as there were many people who could have had motives, including those who knew the victim Elizabeth Short on a personal or professional level.
Yes, perhaps in this fanfiction Bella could be a new Avenger. Fanfictions often introduce new characters or give existing characters new roles within the established Avengers universe.