I probably have no bis in this area but a quick question . I just spent a long day on the back of an old D 17 pulling an 8 foot mower . The owner said he's has a lead on a 10 foot mower (Bush Hog ) . This grass was heavy in a few spots and had to downshift to 1st in high side ... sorry I speak truck driver so if I used the wrong terms please forgive me . This is a gas engine tractor and with it in low gears already is it possible a 10 foot wide is to big for this machine .
Depends on the grass and how fast you want to go I sometimes pull my 10 with m 55 hp utility tractor but usually just clipping a pasture real thick grass makes my 130 hp tractor bark but it can pull it faster than the mower can cut. A D17 gas should be around 65 hp if I remember correctly I would think it will handle it in fairly thick grass just slower than say a 100 hp would. Remember you don't always have to take a full deck width once you make the first cut and the extra overlap usually gives a cleaner cut.
We always go by the 8-10 hp per foot of brush hug.
I run a 6 ft hog on my D17, we've used it on ten foot tall scotch broom and berry vines, but even thick grass makes the tractor snort at times. I think a 10 footer would be too much except for light trimming of grass. An 8 foot flail would be nice to have.
I have a 170, basically a newer D17, same motor and transmission with restyled sheet metal, factory 3 point hitch and live hydraulics. I have a 7' Woods mower. That is plenty big to my way of thinking a D17 is more like 54 HP.