Actually if the vehicle you were asking about was the 1978 its a non issue. Cats were in their infancy at that that time and used coated pellets that failed at a staggering rate and sometimes a new cat was not available for quite some time.
There was a directive in that era up to 82 IIRC that it was legal to hollow it, install an other illegal test pipe if the part was not available due to shortage or the car was owned by military personal going abroad.
Asking how to do it is a fair question in this case and those old cats could not be just bashed out.
It was a 2000 Lexus ES300. Reason was he didn't want to pay $800 for 3 aftermarket cats.
It was a strange thread, several posters were in favor of hollowing them out and I was in the camp that it should be fixed or junked but got flak for it even though hollowing them out is illegal.
Still annoying when they disappear without notice. These types of threads always eventually run their course. There were also some tips in there on how to diagnose it.