The dash doesn’t need to be removed but you will have to remove the glovebox to remove the vents. It will be easier if you remove the dash pad. The heater/AC box in the engine area is not that hard to remove either. Once removed, clean everything since it will be dirty and dusty from 50 years of zero maintenance. Once cleaned, it will be like factory original. During assembly, get some shiny hvac tape to seal up the cracks and crevices, you will also need to buy some thicker weather stripping for some connecting areas so it’s better than factory.