Yes, whether it should be ported vacuum or manifold vacuum is
determined by the vacuum module on the distributor. There are numbers
on there which can be used to identify it.
Mechanical only were done as high-performance items because it allows
the points plate to be bolted firmly in place, yielding a more precise
spark (all other factors being equal), and race cars do not need
vacuum advance as they should not spend much time in a part-throttle
I agree with derf that it is a bit silly to not have vacuum advance on
a street car as it can improve your emissions and your fuel economy
without compromising performance.
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