I did my 72 box. I used a Spectra heater core and the fit good. Gaskets from DMT.
If you want to save the original core then Bob at GlenRay is the best.
I used to be next to Rich the heaterbox guy at Carlisle. He does really nice work.
It does not need to be factory for Bob to do it. If you know the one in the box fits he can recore it. I just sent a core from a 63 that is not original and he said no problem.
