All factory bellcrank pivots have a hex base.
What pictures are you referring to?
In the picture in
THIS LINK you can see what the 1941-62 pivot looks like, 1938 is similar but has a bigger hex and a nut on the outboard end to hold the arm on. The hex in the block in this picture is a 1/4" pipe plug I used to replace the missing mounting position on 1960-62 engines.
