He was? That's awesome.
I didn't know the Rock of Eternity had incalculable weight either, but Cap did say if it was destroyed it would destroy the universe.
Since Cap is able to lift it as well as Mister Atom, then its safe to say GA Cap is already at least equal to his Silver Age counter part.
In this thread, it is apparent now that Cap forcibly takes Thor's Mjolnir, and comically bonks him over the head with it. KO'ing him for a hundred years.