With the castle nut, a lock washer isn't used. It should be bolt, clamshell and castle nut. The two side pieces are a bolt, then the two pieces of clamshell, lock washer and plain nut.
If I remember correctly, one bolt and nut are reversed from the others. I think it has to do with installing the cotter pin. I will look and see if I can find where it shows that. I believe 31tudor is correct as far as the lack of lock washers when using castellated nuts and the plain bolts on the sides with lock washers.
Rusty Nelson
The attached pictures shows how I installed the clam shells on my coupe. I am not 100% sure the bolt and nuts are correct, but I think so.
Rusty Nelson
The picture that Rusty posted is exactly the arrangement that I found when I took mine apart a few weeks ago, right down to the top bolt coming through from the ****** side, and the rest going in the other way.