its the sizes of the primary and secondary venturi. Primary 32 / secondary 32. Tom did say a 32/32 would be ok with a 261 maybe he never understood what mods i would be doing to mine thus not suggesting to move to the 32/36. But with it being bored over min .040, new cam, intake, headers and hei i might just opt for the 32/36 carbs. I read that they are way more user friendly to adjust and replace jets if required. I love the box style air cleaners the most. It add a little touch of modern to the inline sitting under the hood.
