Just trying to be helpful here but I have access to a lot of equipment and none of it gives me the ability to mow that high. An old sickle bar mower on a taller (rowcrop type) tractor might.
I would suggest if you are set on a monoculture of sun hemp then roll it down / drag it down end of august and top sow your fall plot into the mat. Till it all in next spring when the fibers have had time to decay. Otherwise a turning plow might be a better choice than a tiller and plow in the direction of the crimp