15.Composite panels may be used but only if originals are no longer available – all cars must weigh in at a minimum of 90% of their factory curb weight.
16.A roll cage to MSNZ specifications must be fitted.
17.Interior trim may be removed but door cavities must be covered. Aftermarket dashes may be used. An approved race seat and harnesses must be used. Passenger and rear seats are not required.
that sounds like room for ripping everything out and balancing the car as long as its to curb weight is factory, useing steel weights n stuff in the frount and back