I believe you can get castellated nuts that are thicker--I am pretty sure you can for tie-rod ends and other front-end parts, not sure about spindles, but it is either a thicker washer or a thicker nut because you do want to keep it from backing off with a cotter pin.

R-Bo

1959 Apache 1/2 ton Big Window, Short bed Fleetside (under reconstruction)
1966 GMC 305V6 in the family