For anyone in the future looking to replace the evaporator core...
There is a mesh screen on the clean side of the evaporator core. You MUST transfer it over to the new one. Why?
Well, you will get water droplets in your face with the A/C on.
I learned the hard way (3rd time pulling the box), and worst of all, I tossed the original mesh screen long ago. It is no longer available from DMCH. Some GM dealers still have one laying around but with them being discontinued, you are unlikely to find new in the future.
In my case, I decided to drive to my nearest junk yard and pull a screen off a Chevy Astro/GMC Safari. These newer screens are secured with plastic barbed rivets that catch in between the evaporator fins. More than half of GM vehicles from the 90s-early 2000s have these new style screens.
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Trimmed Astro mesh screen on DeLorean evaporator. Notice the push pins.