The cast iron pistons do weigh more than aluminum, they also take more time to warm up and fit the cylinder than aluminum. The amount of force put on the connecting rod is greater with the cast than the aluminum. If the engine gets hot enough to stick the piston to the cylinder wall your going to have bigger problems than a piston dragging against the cylinder wall. If it starts to stick to the cylinder wall you can figure on a bore job with new pistons at the least. I you ease your truck up to speed you should have no problem. I drive my '50 216 50 - 55 and just take it easy, once up to speed things go along just fine. With a bigger truck you may be a bit slower. Just take your time getting it up to speed.
