Kinda sounds like compressor surge. Are the turbos fighting each other somehow?
Is there still a blow off valve?
(I don’t know what I’m talking about, just spit balling)
Don’t need a cert to switch to flat deck/send it.
Dimensions: https://vehicleinspection.nzta.govt.nz/virms/in-service-wof-and-cof/general/vehicle-exterior/dimensions
(see tables and images)
You can have 4m past the rear axle.