The .520" may clear, but never assume and always verify. It will be close, whereas the .470 will be certain. You can just use Comp #901-16 drop in springs with that. I have the 270S (224*.468: before lash) with those and zero issues, even at 6500+ in my 318 (328"). You may have more installed height with the RPM heads, so don't give up on the .520" Howards before you measure or have it done!
