As Mike says, generally you cut the old column outer tube leaving the inner shaft longer than the tube. This is done to a length to accommodate your new column. You will grind two flats on the old inner shaft to receive a coupler (straight or universal joint style). This is called a double "D" shape. The new column will possibly have this shape also. It must be all measured so that the coupler of choice will connect the two (old and new) shafts together.
Here is a bearing for the old shaft to support the inner shaft after cut....or make your own. Lots of info on the internet about this swap.
http://www.classicparts.com/1947-59...Bearing/productinfo/76-987/#.V5Zce-n6s5s

Approximate example from Ididit:
http://www.ididitinc.com/pdf/55-59ChevyTruckColumnInstallInstr.pdf

Another:
http://www.jalopyjournal.com/forum/threads/stock-steering-column-conversion-bearing.447979/

You can also use an "intermediate shaft" to span the distance or as a way to angle the shaft. This is just a piece of double D shafting.


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