Angle cut the two 82-inch legs at the top at 15 degrees. Measure 78 inches from the bottom of both legs and on the widest part, drill a 3/8-inch hole through each.
Drill two 3/8-inch holes through the 81-inch rear leg at 39 inches from the bottom and 74 inches from the bottom.
Assemble the legs by laying all three pieces on the ground with the rear leg in the middle. Put a bolt through the holes you drilled in the top and loosely tighten with a washer and nut. With all three legs still lying on the ground, spread the front two legs apart until they are 45 inches apart at the bottom. At that distance, tighten the nut at the top.
Measure 38 inches from the bottom of the two front legs and drill and bolt in place the 48-inch cross member. Glue and nail the plywood back to the front legs so it is resting on top of the cross member. When the glue is dry, stand the easel up and spread the back leg out until the easel is a workable angle. Tie the rope through the hole you drilled in the back leg. Insert an eye screw into the cross member and tie the rope off.