What other species can you dry with 5/4 black walnut?
Green or air-dried? If green, then look for species that have the same last number in the kiln schedule and the second alpha character within one.
For example, T4-D2 (for red oak) can be dried with any that end in "2" and have the second alpha character of C, D, or E. For air-dried, they can be further apart -- both number and alpha.
"Drying Eastern Hardwood Lumber" lists American elm, slippery elm, holly and mahogany as similar species. Birch would also work.
Gene Wengert, forum moderator