I bought a used 4520B BH attachment for $2500. I know I can attach it to my B7500 via 3PH, but I go back to the sub-frame debate. My 7500 has a 60" mmm. I will be the only operator, and I am very nice to my tractor. The BH will be used for trenching and digging around stumps near Lubbock, Texas. The ground is hard pack caliche with few if any rocks. The 4520 comes with a "modified" sub frame (I bought the set-up from a welder).