Read the Testers manual. If the car is special purpose then they DON'T need to be adjustable. Mine will be bolted to the floor.
https://www.gov.uk/government/public...and-7-vehicles
The relevant passage: Section 6-2
"Original Design characteristics and specialised modifications (e.g. to enable wheelchair access) are to be accepted."
Cite original design characteristics. If it passed the IVA that way then that's original design.