My current Dearborn Built '65, DSO 61, had its Engine stamped with an early December Date Code 4M7V, which I understand to mean December 4, 1964...it has a Road Draft Tube - surprised me when I first saw it.
I had another '65 6 Cylinder, DSO 31, built in the same month, but it had a PCV Valve. At the time, I didn't think anything of it as that is all I'd ever seen. Unfortunately, my photo record of that Engine is minimal so I have no good way to make any comparisons between the two that would give me an indication of why a Draft Tube on one and a PCV Valve on the other.
Maybe Ford found a pile of unused Draft Tubes and was just using them up or maybe they ran short on PCV Valves, or was there an Elevation above Sea Level Issue, or did Doc and Marty travel back to1964 and crash into the PCV Valve Factory...who knows.
Ray