I do not have a 300, but would think my older 400 is close in the same size range of it, maybe hair wider/longer, but not much, you need to measure your atv's width and then look at below chart, you want your atv's tires to be OUT of the snow plow blades path, extra is better than less here IMO. plow more often before getting too deep and you will be fine too!
I run a 60 inch blade and a push tube , belly mounted set up using winch to lift, for the past 20 yrs now
Moose makes a universal belly pan mount too, cheap off brand name blade can be just that CHEAP and bend and fail, buy once cry once!
as for a plow size here is a chart off Moose plows
I THINK there blades are GREAT blades too, mind has taken a beating for the past 20 yrs now and still holding up great and I am FAR from easy on it
Path cleared when fully angled