I am thinking about a hunk of railway track (120 lbs/ft) 5' long and a piece of 1/2" plate steel on the opposite side for reinforcing. That should make it heavy enough for grading. Total weight should be about 7-800 lbs.
Rail isn't that heavy. Maybe it is about 120lbs/yard.
From:
Rail profile - Wikipedia, the free encyclopedia
Some common North American rail sizes include:
75 lb/yd (37.2 kg/m) (ASCE)
85 lb/yd (42.2 kg/m) (ASCE)
90 lb/yd (44.6 kg/m) (ARA)
100 lb/yd (49.6 kg/m) (AREA)
105 lb/yd (52.1 kg/m) New York Central Railroad
115 lb/yd (57.0 kg/m) (AREA)
119 lb/yd (59.0 kg/m) Colorado Fuel and Iron
127 lb/yd (63.0 kg/m) New York Central Railroad
132 lb/yd (65.5 kg/m) (AREA)
133 lb/yd (66.0 kg/m) (AREA)
136 lb/yd (67.5 kg/m) Colorado Fuel and Iron
140 lb/yd (69.4 kg/m) (AREA)
141 lb/yd (69.9 kg/m) (produced by Nippon (Japan))
155 lb/yd (76.9 kg/m) (no longer in production) Pennsylvania Railroad
or more detail:
RAIL SPECIFICATIONS
Bruce