A short motor comprises a block, crankshaft, conrods, pistons, rings, bearings and windage tray as a balanced, clearanced and assembled package. It does not include the cylinder head or sump, and subsequently is "shorter" in stature than a complete engine, hence the term. A long engine is just that; a short engine with a cylinder head, valvetrain, rocker cover, camshaft drive system, oil pump, timing cover, harmonic balancer and sump fitted. All you then need to do is fit the external accessories, such as manifolds, alternator, engine mounts, etc before re-fitting to vehicle.