Big block swapping a 1964 barracuda

I’m just over an hour drive from a place called mopar city so I was gonna call tomorrow and see pricing for a manual steering box and the rest of the drivetrain I need, and how big of a tube for the primary tubes? From what the guy I bought the motor said it’s a freshly rebuilt 383 with a unknown spec purple cam

I'd go as big as will humanly fit in the thing.