As you likely know Marlin didn't classify barrels with a number for the contour. Most fall close to what Winchester numbers are, but not exact. 
Often barrel contours depended on the cartridge designation, and the larger the bore the bigger the outside diameter. But then I've owned some early JM Marlin Ballards in small bores with very heavy barrels too. Seems more likely to see heavy barrels in the JM Marlin marked Ballards than on the Marlin Firearms Co. marked Ballards. The largest Ballard barrels I've seen were mostly on the Montana model and are about what I'd call a #5 Winchester barrel. A few Pacific models also got ordered with a similar heavy barrel.