[Kube]

Fred,
As you no doubt realize, it is nearly impossible to determine exactly when any 1940 was built without authentic documentation. Including all of the '39 & '40 Fords I have owned, only three have had irrefutable proof as to when and how they were built. We can however, using a number of telltale signs, offer a good approximation.
The car you have with the "5444" had the engine mated to the transmission and it's serial number applied in the middle of Dec.1939. Your car with the "5304" number is obviously an earlier build. Its engine was mated to a transmission and the serial number applied in mid October, 1939.
That being the case, it is a near certainty that the "5304" car had the first design ash trays. The "5444" car most likely had the early design as well.
The ash tray design was changed in late January, 1940. How quickly that change was put in to effect at all of the assembly plants is a question we will likely never know the answer to. Typically, fairly quick...
If you want to do these cars as correctly as possible, I'd suggest the early ash tray design for both vehicles.
And by the way, the two places the serial number was stamped to the frame beneath the body did not receive a prefix - in your case "18".
Hope this helps...
Mike "Kube" Kubarth