[budge96]

Either of those two differing materials will suffice and still maintain period correct stature ..
however one may perform its duties altogether differntly than the other the former of the two plastic covered flexible material has an aluminum insulated interior hose which will carry heat to the thermostatic pipe on the mechanical injection pump.
The latter of the two with the aluminum sheathing to the outside may also function just not to the higher rate and speed of the former..
The cold air flap your referring to actually is meant to provide warmer incoming air to the intake and convert to less warm as idle rises.
your car will function without it ,not absolutely necessary for a well running example but necessary should you be aiming for some concour
or contest of originality.
thanks Bert