That definitely sounds like enough work to be using something on the 3pt rather than the FEL especially if you're working on a tight timeline.
While I don't have experience with any of the following they're manufacturer's I've considered buying from myself:
MonroeTufline, and King Kutter might be options for box blades/rear blades (Monroe Tufline also has a line of wheeled box scrapers which may be of interest/use), alternatively a "small" (1.5-3 yard) dirt pan by Hoelcsher or Durabilt might work as well if there's room to maneuver a pulled implement.
Of course depending on the rental market in your area, it may also be possible to rent either/both implements (potentially without having to rent a tractor as well) --- or even rent a stand-alone piece of equipment that could do the job (e.g. skid steer with a harley rake, or even a bulldozer), and with larger equipment it may also be possible to have it delivered/picked up as well. From past experiences I've seen that it's possible (around here at least) to rent some really heavy/capable equipment for a week for less than some new/used 3pt implements cost. Just another option for solving the near term problems that might make buying something to handle the long term maintenance cheaper/easier.