Need a good flush

Want to flush my cooling system on my 1954 Cadillac. Radiator was rotted a few years back and the engine was rebuilt also a few years back by a friend (since departed). I don't know if the block water p***ages were cleaned good during the rebuild so I hoping to do something now to insure that I don't have a film on any of the internal surfaces of my cooling system. Is there something better to use than the off the shelf flush (such as Prestone)?

 

Somehow I thought there would be some advice out there on cleaning up a cooling system.