Welcom Back!!
Go with something in a 19" top tube for shure I used to flat in the mid to early 90's.Yes alot has changed,Do you want to buy a complete? or build a custom?
Custom would be the way to go, But I don't know your situation.
Most of the freestyle frames now are very short overall as compared to the 80's 90's.
When I got back into it I bought a KHE Stylus complete bike which is 18.75 top tube i think, Sitting on it felt very cramped but you get used to it, I'm 5'11"
So at 6'4" go with 19" or more top tube (of the frame) everything else, All the other parts is basically preferance.
Oh ya, Only buy from FlatlandFuel.com!!!!!!!!!