The IT shop manual FO-4 says on page 31" tighten connecting rod nuts evenly to a toque of 35-40 ft.-lbs., then install new locknuts(pal nuts) and tighten to 4-5 ft.-lbs. torque.
The May 1950 parts book describes the nut as 3/8"x24 hex and the locknut as 3/8"x24(9/64 x 9/16")hex locknut. the locknut is about half as tall (or less) in the depiction.The March 1994 Assembly Manual and Service Parts Catalog doesn't list the locknut.
I guess locknuts make the most sense to me, but why does the newest parts manual omit them. Is red locktight good enough?