Excuse my loose use of terms. These nuts are neither castle nuts, nor castellated nuts. I called them castle nuts because the end of them look like the top of a castle.
The castle portion of them are crimped slightly inward to deform the threads to make them lock. Once installed, the single hole in the end of the bolt for the cotter pin does not match up with the castle end of the nut. Too far away. Even if it would engage with the castle end of the nut, you would either have to strip the fine threads, or leave the nut loose to make the pin engage with nut. Trust me, you do not want to leave them loose.
As I mentioned earlier, I have some unused replacements which look to be NOS, and they indeed do function as lock nuts.
BTW, I did use thick flat washers under the lock nuts.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission