Nah, I doubt it would have weighed that much, those engines are pretty high performance, not much different than what is in a top fuel dragster really, likely aluminum block, and lightweight. Still 400-500lbs I am sure with everything on it...but no where near the 1000lb mark.
I would say by looking at the wreckage, the block split in 2. If the block separated from the oil pan, it would have taken the crank and pistons with it, since the engine block itself encapsulates those parts.
The tractor pull guys work their tractors much the same way as the top fuel and funny car dragsters, and the engine gets torn down between each run, likely the aluminum block had a fault in it, and once the power was put to it, sheared the block off at the bottom of the combustion chambers, thus leaving the bottom of the block, crank shaft, pistons and rods in the tractor.