Here's what i could find for the reversible airflow models. Let me know if I missed anything.
Fan Item# Part # Dir Switch models
450300 17111 F->B X670/V, X670-G2, X770
450326 17112 B->F X670/V, X670-G2, X770
800560 10945 F->B X460-G2, X450-G2
800561 10946 B->F X460-G2
Don't forget that the PSU must match airflow as well. I can look for those numbers if you'd like.