the firewalls are all the same, but the holes are specific to the model of heater, and for 57 there was at least 3 different ones, all with different cores - if yours had a non-GM heater, the holes were done by whoever put that in, not GM .... if you've still got the original inside "dash mat" you might see marked-but-not-punched circles where different configurations would go - CDN will be the same as US
Bill
