I have much, much larger tractors than most posters here, but a good rule of thumb on width of
any implement is to buy the widest implement that will clear the outside edge of the sidewall of the rear tires at their most outset position.
Example. If the rear width of your tractor is(measured from outside sidewall to outside sidewall) say, 58", then you should by an implement width of no
less than 60".
Remember, wider implements, especially those that engage the ground consume more power and require an initial heavier, more tractive unit the wider they get.
A good example of implements is my Lucknow 78" rear blower that I had on my
L5030 that's now on the M9. Maximum
outset sidewall to sidewall outside width was 76" so the 78 worked fine as it was 1" wider than the outside walls of the tires and allowing sway in the 3 PH linkage, was right on. The M9's Minimum
inset sidewall to sidewall outside is 78", That's inset not outset. The 78 can be used with the M9, but the M9 is technically overpowered for the 78. This summer, I'll have to extend the side sheets of the 78 to at least 80" or get another, BIGGER, blower. If I modify the 78 to at least 80", I still have to watch how I push the blower as the M9 has at least 30 horses more than the maximum rating of the 78 which is 50.
The rule-of-thumb works for all implements excepting backhoes and other hydraulically operated devices. with those devices, weight of the implement versus how much weight the tractor can carry itself without structural damage is the limiting factor.