Heater core re-cored? Or such thing as a universal one?

I'm yanking the AC stuff. It's gone already. But the heater boxes, ducting, and firewall are completely different.

I suppose if I had a non AC dash and vents...But I don't.

To make all this that much more silly, the core doesn't leak, but looks rough.

So I hoped to replace it, use the AC box, and all would be well. It just wouldn't have A/C

So fill in the firewall holes and put somethin like this in it.

Car Universal Under dash Heater Heat Defroster Demister W/ Switch 12V 4 Ports | eBay