No such thing as totally closed, the crankcase needs ventilation. So its either a PCV system or a road draft tube. For 66, most cars (here in Australia) still had a road draft system with a tube from the block. From 69 we have a PCV system to reduce hydrocarbon emissions, I would imagine the USA is not much different. If your block has the road draft hole in the front you can plug this and run a PCV system which is better in my view. If your going for originality you can run the road draft tube and put up with the fumes. The blow by should be minimal for a new engine such as yours. IMO I would go with the PCV setup.