It depends on how your top end went out?? Did the piston break into pieces? Crankshaft bearings let go into pieces? If stuff falls down into the bottom end then you need to get it out. If the piston siezed or rings got stuck then you could prolly get away with a topend rebuild.If i were you, while you have the top off its a good idea to redo bearings and seals and gaskets to make sure it dont happen to you after a new topend!!