consider this, heat kills coilpacks. any coil setup as a 'coil on plug' arrangement are sitting right in the middle of the engine, yes? how much heat do you think theyre exposed to? ever touch your cam cover after a spirited drive?
the beauty of the GM/ford coilpack conversion is that they can be remote mounted, away from the engine, and shielded from heat. the lines from the coil pack to the spark plug itself can also be heavily shielded from heat.
the next and most obvious advantage is cost, call up your local holden spare parts department and ask for the price for 3 vn coilpacks (3 is all you need for a 6 cylinder engine) and then call up your local repco/supershit/sprint auto store about a set of leads, youll be pleasantly surprised.
(note: ls1 coil pack conversions require 1 coilpack per cylinder as normal)