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In the disassembly video you were commenting on the split on the piston skirt. For sure that was present on the prewar cars. I'm not positive on the postwar models. I believe the splits were all placed facing away the direction of travel of the crank. So the solid side of the piston was the side getting beat against the cylinder wall as the crank moved around. The split was facing the valves. I can't speak for the specific reason behind the split pistons. I'm sure someone with more knowledge will chime in.

The split skirts were necessary to control expansion with some aluminum piston designs.

It must have taken quite a bit or rebalancing with all these changes to make it smooth and quiet!

Many of Packard pistons (at least the 288/327/359) also had an expansion strut in the pistons. They were heated, and the strut was pressed, which then reduced the contraction when cold. So in a sense they were pre-expanded.