Taken from the WA Dept Transport website:
Modify a vehicle
...Modifications that don't require approval
Many minor vehicle modifications can be carried out without specific approval, as long as they comply with the applicable legislation. Modifications that don’t require approval include:
Additional lighting
Air conditioners
Air shock absorbers
Alarm systems
Badge bars
Body markings and speed striping
Gearbox (pre 1976)
Mesh stone shields for wind screens and lamps
Mud spats and pebble guards
Optional manufacturer seating
Radio and stereo systems
Rear-view mirrors
Roof racks
Seat belts for pre 1969 cars (no full harness types)
Single tone air horns
Stabiliser bars
Sunvisors
Torque rods and traction bars (not semi-tramp types)
Tyre size and aspect ratio
Venetian blinds and other internal screening systems are allowed, subject to a clear view to the rear...
Seems OK to me to fit seatbelts in WA without engineer or other approval...
(Sorry for the thread highjack mfc).
Cheers,
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