Why am I drawn to the aluminum??

The pedestals assure that the Indy/RHS will work on either LA or Magnum block based builds. the fact that the heads have both are what makes them so heavy. They've got two sets of rocker pedestals...
In terms of pistons: No - A piston with a deeper valve relief is a smart upgrade which is why Brian recommends them. You don't need CP custom forged...or any forged for that matter...lol - those are an extra cost that IMO isn't needed. But you need a performance piston with valve reliefs to run any decent sized modern camshafts. New pistons mandate a bore/hone and also balancing the rotating assembly. Another IMO smart extra-cost upgrade would be to internally balance it since it has to be balanced anyway... (See how these things start to creep up...lol)