You don't need to logbook a car for sprint.
There is a General Requirement for car and drivers here
https://cams.com.au/regulations/manual/general-requirements
I am pretty sure for sprints any seat is fine provided it's mounted correctly
With tint 'have any window or windscreen fitted made from a material which is clear or, if tinted, compliant with AS 2080;'
If you have a cage it probably wise to register it with CAMS because they do change their cage requirement structure from year to year.