If i was buying a GC8 with a 34/205/FMIC .. First thing i'd be doing would be wacking it on the dyno to see where i stand.

If the AFR's were all over the place and shit didn't look good an aftermarket ECU would have to go in and iron it all out so you've got a nice clean tune which is safe for the motor.

A 34/FMIC/205 will go good, no doubt about that, you'd just wanna be sure that it's got the an uprated fuel pump/injectors (duty cycle) to ensure it's not running lean etc.