You many want to consider that, this is one of the more abusive pto driven implements you can attach to a tractor. Depending on the conditions, what you will be cutting, and or the hidden, unforseen rocks, objects or the worst case scenario, any stumps and all the rest, that it either slips properly via a slip clutch or it shears when it needs to. I saw a very expensive repair with a JD 2020 last year, which I now suspect was an unknown, possibly grade 5 or 8 in the driveline of this old but really heavy duty rotary mower, it destroyed the shaft coupler, and it was a split and complete tear down, for a very inexpensive bolt, pin or slip clutch.
My old Rhino has a shear pin hole in the drive line and I use shoulder bolts with left hand thread that shear, which have nylon line nuts, these will shear before a grade 2 bolt will in the drive line, it will lay both blades down under the deck, with the remains of the hardware, last time it was a hard round rock, that surfaced the last time the field was in crops. The blades are connected to a blade holder that has as stump pan, no doubt those pans can help reduce some impact. I ran a tail wheel through this mower, and though I did slow it down quickly, the grade 2 nor the blade bolts sheared, it did a lot of damage to the deck, another 50 cent pin, that failed, cost a lot more in repairs, should have been replaced, it got past me, new tail wheel, and a bunch of labor to straighten the sidewall of the mower and a bunch of miscellaneous welding to the deck, caught some welds on the blade holder that would have failed, wish that grade 2 or blade bolts sheared that time! Not to mention if it was paying job the down time over a darned 50 cent pin.
I've taken saplings and heavier brush/bushes, starting up high and lowering into them in the succeeding passes, in 12 years with this mower, I have sheared that grade 2 bolt one time as I recall, it does fit nicely too, no slop. I think the best advice is to play it safe, they can do some damage in short order per the above. If you are dealing with a lot of conditions where it will impact and shock load the drive line, don't have a stump pan, I'd seriously consider a slip clutch, make sure it works correctly or get a pile of grade 2's to keep on hand, at over 3K in repairs like the above, and or depending on what you have for a tractor, something to consider, that buys a lot of bolts/pins and or slip clutches.
Another thing, depending on what you are running for a mower, with so many different kinds out there, the book for it may provide the specifications of what should be used anyway, one page in the book for mine certainly helped me avoid a lot of problems, as well as making it perform as designed etc.