Frank Sinatra wasn't even that much of an actor, I'd say he's more like a lawyer/diplomat/spy kind of person, LOL!
Elvis was in the line of James Dean, the way River Phoenix was after Elvis and they way I am now. I'd say Elvis was probably least confused and ashamed of everything among these people, because he knew love as a child.
Anyway, yes I think Elvis had the talent to do something with his acting abilities. It's just that Hollywood was the wrong place, just like Las Vegas was the wrong spot for a musician (Las Vegas = showbizz, not music).
He should have met John Cleese. At least Elvis did enjoy "Monty Python's Flying Circus", LOL! I'm talking real actors here, not the showbizz-bullshit you see at the cinemas nowadays.