You can stunt a boas growth to a certain extent... basically feed them once a week until they reach 6, 7, 8ft then reduce the prey item down to once every 2/3 weeks and they won't get much bigger.... as for little box little snake, thats total crap!
Basic i.e. min requirements for a boa is 1 sq ft of floor space to every ft of boa... That is what I would call a min requirement though, obviously more is better