I would use the same leveling method the Romans used to build the giant aquaducts, roadways and buildings 2000 years ago...the simple water level.
Get a clear piece of plastic hose, fill it with water and then lift one end at your benchmark. The other end you hold on the other two legs and mark them. Since water always seeks its own level, you got your level problem solved.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"