Can't improve on the advice given so far. I bought too light and "made do" with added weight. After many years of using a variety of box scrapers, I decided to bite the bullet so to speak and bought a Land Pride HR3584 to use on our tractors and put Top and Tilt on one of our tractors. The cost was a bit hard to swallow, it it was worth it. Other box scrapers are as good or better than mine, but it is what my dealer handles and I like LP equipment.
I guess my only advice is to buy the best box scraper of an appropriate weight that you can afford and seriously consider adding Top and Tilt.
Mine is considerably wider than my tires on our L5740, but I also use it on our M8540 and it covers the tread.