i recently aquired a compact 4WD tractor along with a 3pt mount BH. Since then, I have designed and built a subframe so as not to over stress the lift arm and top link anchor points. chances are the tractor specs require a subframe.
if you use the unit for occasional light use, a 3pt mount might be okay. for commerial and/or heavy duty use, seriously consider a subframe.
best regards,