I remember when custom gunsmiths would rebarrel a Smith with a larger diameter " target " barrel, a few left it heavy bbl. style but most slabed the excess off the sides of the barrel. I seem to remember Jim Clark , Clarks Custom Guns, doing his Custom Combat Conversion that featured a Douglas bull barrel and could be had full diameter or slabsided...
I am sure they still offer the conversion, I just can't remember what year all this started. Now the factories offer them right off the shelf. Clark's conversions looked really good , the old master knew what " good looking" was .
Gary