Chiming in on an old thread: Mine (Aug 2020) also specified regular undrilled AN7 bolts and MS20365 metal lock nuts. I'm curious about what would cause Vans to change this specification, because I'm sure I've seen builds with castle nuts + cotter pins for these fasteners. Perhaps my mechanical knowledge is way too rudimentary, but I've always thought of cottered castle nuts as "more secure" for whatever reason.
On a separate topic, I noticed that for the mount-to-firewall bolts, for -A configuration, at least -7A, Vans calls out undrilled AN6 hardware and AN365 nylon lock nuts (on the cabin side); whereas for taildragger configuration, Vans calls out drilled AN6 bolts, cottered castle nuts on the engine side. Curious.