The shaft and box are one piece, how have you removed the box and not the shaft?
If you are talking about the outer tube, it is bolted to the bottom of the dash with a u-clamp and special holder plus there might be a clamp at the floor board.
If you really want the shaft out of the gear box, read this manual,http://chevy.oldcarmanualproject.com/booklets/52mts20/5220mts01.htm
Once you have the tube out of the cab, use a broom handle or the steering shaft to knock the bushing out the top of the tube.
Its best not to destroy the gear box, guys like us with the older trucks use your modern gear box to replace our old style ones.
Joe
