My factory 5.0 block can handle over 1000hp, its not my fault that everyone else use the crap ones.
Less weight, aftermarket is pretty darn good, will fit in a lot more engine bays, nothing like a 5.0 strocked to 331 reving to 9000rpms all day long
5.0 will be more than 100lbs off the front end, over a 351C, so throw a few turns, and the 5.0 will say bye bye. Straightline, the 351C is pretty darn good.