Aluminum /6 Rear Main Seal
You're correct: there are additional pieces in the aluminum-block rear main seal kit not needed (therefore not present) in the iron-block kit. You'll have to find these pieces from a gasket specialist (Hemmings lists several who have hooked me up before) or goop it with RTV and hope for the best.
Also, you know you need the special aluminum-engine head gasket, right?