Rebuilding heater box, replace core?

One of the 3 heater boxes 1 that I had ended up as a "donor" heater box, between the 3 of them I have just enough good usable parts to get 2 good functional clean and leak free units. Between the 3 that I had, 1 had a cracked box from rough handling/disassembly, 1 had a cracked top around a vacuum pods, 1 had what looked like a heater core just ready to go, ( judging by corrosion that 1 had, that the other 2 didn't) and 1 had a blend door that was so rusted under the foam it was unusable
I did have to open up the mc master carr catalog and buy some replacement foam for 1 door in each good heater box.that does not come with the DMT kits and he will tell you as much on the site and on the phone.