Port add on for sure, factory heaters though available starting in late ‘64 didn’t be come standard until till ‘66 though most ‘65 had them. There was a factory option heater in early 40/45s it was the Denso “clam shell” and was Uber rare mostly seen in ‘63 FJ45LVs
I would agree on a lot of cross over parts on the early. My 63 has the metal ribbed top but I just had a 64 fixed top in here that was metal and had no ribs. It’s the second one I have seen with no ribs.
my 63' has a ribbed steel roof and my 64 has a smooth steel with no ribs (also sold a 64 no long ago that was the same)