Yup, you are right.
IMHO it was probably sufficient because this car was driven in normal traffic (well, normal for the sixties) so I assume it was built accordingly. Besides volume of sucked air seems to be proportional to rpm so you can floor it if you need more cooling
But, I am not an engineer.
I agree it is not practical though. No muffler, 105 dB at cruise speed. Police would love it for sure.