As I mentioned in a previous thread, I've had an issue where the car would just drop out randomly. My only pattern was i was turning right and braking. Took it to Holden (useless ####s) 3 times, and it wasn't until NRMA mech came out for a breakdown where it was finally fixed. Meanwhile, I had already replaced alternator (x3), battery (x3), leads, coil packs, DFI module, plugs, etc.
It ended up being the bracket that holds the alternator. The one that bolts to the top of the engine (long bar one, to the top of the supercharger in my case). It was put in the wrong way and was causing the alternator to short from the B+ terminal on this bracket and then stall and prevent start or crank from the engine. Give that a go, since it's free and remove that bracket, check for any evidence of shortage (seinfeld joke just came to mind) and if so, remove the bracket and place insulation between the terminal and bracket if you intend on keeping it.