There is no hydraulic down pressure from the three point hitch. Gravity provides all the down pressure. Therefore, for a Box Blade to cut, you need a lot of weight. An "ideal" weight for box blades is 150 pounds per foot of width. If you are too much under that weight you will likely be disappointed with the performance of a Box Blade scraping hard soil.
What tires do you have? The 50.7 inche width is for ag tires. If you have a Front End Loader, you probably have Industrial Tires which are 2"-4" wider.
With 22-horsepower to work with I would buy a Box Blade close to the ACTUAL width of the tires on your tractor.
For "spreading and grading gravel and topsoil" consider a Landscape Rake or a Rear/Angle Blade in preference to a Box Blade. Both are commonly used on an angle and will move material across the face of the implement. Both will likely give better performance for "spreading and grading gravel and topsoil" on your 1,700 pound tractor. A
heavy Landscape Rake would be my first choice, such as Land Pride LR16 series.
As Landscape Rakes and Angle Blades are used on an angle most of the time, correct width is 10"-12" wider than your rear tires.
All three implements will work better if you have a Front End Loader to counterbalance rear implements.
LANDSCAPE RAKE LINKS:
https://www.google.com/search?clien...+rake+site:tractorbynet.com&ie=UTF-8&oe=UTF-8