The 1940 adjustment screws are 10-32 X 1-1/4"L as measured from under the second head, made of steel with a slotted pan head. Would be easy to solder a washer under the head with a gap of 1/16" between the two heads.
If the engine had no ground there would be no spark. The voltage at the coil terminal varies from battery voltage to about 3.5V depending upon if the distributor points are closed or open=6.5V
If you suspect no ground add a temporary ground wire (#12 AWG) to the engine and see if you then have...
Heads for 40 marked "F" are aftermarket. 40 car 85 HP used the cast iron "A" head which also has Ford part number on the upper edge. This head was used by Ford since 38 and there are modifications to the head over these years.