73-87 a/c parts on 67-72

[project1971]

Has anyone attempted using 73-87 evaporator cases on the 67-72 firewalls? The toying i have done with it i know some modification will have to be done to the back of the case as it sits higher then the firewall. The reason i am looking at this is the evap case i have for mine it pretty trashed and can't find a new one anywhere. I can find EVERY other piece for the inside but not the outside case. Any help would be great either with the mod of new case or place to buy a new one. Thanks!