as the cars before 1986 (?havent checked the date, i assume thats right) were before the australian design rule which enforced cats.

Pre 75 or 76 means even less rules. And i think pre 73 means bugger all ADR, i think basically all you need is working windscreen wipers and front seatbelts.

The weird thing is I've seen engineers make people put cats on their 1969 1600. I'd be asking where and why.... They are expensive items, if they arent needed :)