Intake Manifold without Pipe Threads for Vacuum port.

[Fullraceflathead]

I just bought an Intake Manifold without any threads tapped in it for the Vacuum port for the wipers.
Would this be an early 1928 Manifold???
I bought it thinking it is an early one and since my '28 Roadster Pickup came with a mechanical wiper it might actually be correct for it.
It does seem odd though that they would have kept engines with and without tapped intakes organized just to match certain Models on the assembly lines when you consider the Volumes of Cars being built each day.