1969 Camaro Heater box question

[Lynn]

JMHO, but this is a really dumb decision by GM to use two different heater box covers and heater cores.

Once they figured out the original small block configuration was going to interfere with the BB install, they should have just superceded and made all of them with the revised heater core/cover. No reason you can't use that one in either application. I have no idea of the additional cost to maintain and install four different parts, but there had to be some cost involved.