I hope I didnt come across as an asshole mate honestly was just venting about some of these workshops and the "expertise" provided.
Try to get some specs on the ATP turbo. Speak to ATP direct and find out what actuator was used and whether it's worth changing rear housing to suit an external gate.
I'd also look into the fuel setup.
One thing that stuck out at me also was the boost controller. At this level of power, you really should be using an electronic boost control solenoid to be able to maintain the boost curve and mitigate against spike or creep which could be dangerous.
Have you managed to log any runs yet with learning view?