Henry Aaron is the newest member of the 500 HR Club and a clear threat to take the top spot over the next few seasons. The blast that did it gives him 40 for the season, equalling his career high with a handful of games to play.
He's an interesting one given his late-ish finish at age 42 IRL, which is usually about as old as the game likes to let them get in this timeline, so I don't see him getting as much benefit as Mantle et al from the relaxed settings. Still, with the Mick pretty much done at roughly 580, Henry should overhaul him and even found the 600 Club before he is done.
