Where to get early A Body Heater Core?? or repair??

Installed a 'Made Elsewhere' one from Autozone for about $40. Took about 2 hrs, non air 64 Dart. Everything lined up and no leaks so far....This was my first time dealing with an aluminum core instead of the brass/copper ones. Couldn't believe how light weight it was. That has surely gotta affect longevity....Another example of getting what you pay for.