I have been doing the same exact thing you are dealing with for ten years.Red willows;this stuff is very tough and gets thick and strong rooted.Forget the tree shear,built one last year;way too slow and really didn't work well on the small stuff(3/4-1-1/2").
I have a similar sized tractor and a 6' new Landpride+ a 5' Bush-Hog branded cutters;you cannot back into it,it just lifts the cutter.
I am like you and don't like driving over 10-12ft..tall brush and scraping the *** out of my rig.
Best advice I could give is hire it done;best rig is a forestry mulcher and then maintain with your tractor.
Another problem with a BH on this stuff it leaves a lot of "pungi" stakes.
A few years ago I hired a fellow with a 100HP tractor and 8ft.BH and let him take all the abuse.I still have lots to do along my fence lines;the property was neglected for 50 years.