The '56 182 is not the same as a late model 180 / 185, it is the same as an early 2 window 180.
Having said that, there have been early 180,s converted to the 3 window configuration, so in theory it would be possible. I doubt there is any way to legally do this in today's FAA... There is a monumental amount of work involved, and it would be more cost effective to purchase a 3 window airframe, even if you already have the 2 window ship...
Take care, Rob