The pilot and a certificated pilot/passenger departed the Rock Hill Airport for a local maintenance test flight following an engine overhaul and installation. About 10 minutes into the flight, the engine oil pressure dropped to zero and a complete loss of power followed. The pilot radioed the information to the departure airport and attempted a forced landing in a large pasture with fences. The first touchdown was about 1,746 feet past a tree line at the edge of the field. The aircraft collided with an earth mound 961 feet past the first touchdown point, rolled inverted, and collided with the terrain 300 feet past the earth mound. The total distance between the tree line at the edge of the fields and the stopping point was about 3,091 feet. The latter portion of the path was more steeply downslope than the first 2,150 feet. Post-accident examination revealed an oil line which showed evidence of not having been properly connected.