The PB out on your new aux valve is needed if the internal
3pt lift cylinder is downstream of the the loop installed as
described previously. If the 3pt cyl is upstream, then it is
not needed. I do not know if the 3pt is up- or downstream,
so I took the safe way out.
As for when you use a backhoe, I have found that the
3pt lift control is easily moved accidentally (bad), I take off
the handle when the backhoe is on.