Not so sure about zvh's, but i had a rebuilt standard cvh engine on omex management with a stg3 t3, ported head/newman cam and solid lifters mapped at 1.5bar which made around the 250bhp mark and lasted a good 2 years of abuse, trackdays and pod etc.
Car went so well for what it was....more boost needed for yours, and imo the head on mine made a big difference, revved so much better and pulled hard to the limiter
As for management, the aftermarket route just opens up a few more options as to where you can take the car to be properly mapped as you'll definately see gains over fitting a generic chip.