I.e is there a single route going up and down each column, or does it travel along the top/bottom left to right. My radiator has twenty set of three columns, would be good to see the inside of such a radiator.
Hot water radiators which are connected together on both the top and bottom have no baffles or plugs. Inside the radiator is one open cave from end to end. The recommended way to pipe a cast iron radiator is hot in at the top and return (cold ), out the bottom. As the water cools in the radiator the water gets more dense and heavier causing the flow to be towards the bottom of the radiator. If you are interested in radiator construction you could buy or find an old radiator and take it apart.