It's possible. It really depends on the design of the OWB. Anthracite must have all the combustion air coming up through the coal bed. No air can be entering above the fire.
So if you have a typical OWB with a solid steel bottom to the firebox, where you shove the fire out of the way and use a shovel to remove the ashes, then you would have to raise a false floor, at least 5-8" above the actual floor, make the new floor with shaker grates, cut a hole in the end of the OWB to make a door for an ash pan to be slid under the grates. Make a door with an air vent to let in air under the new floor.
With the above modifications you could burn coal in the OWB, but you would have load of coal around 200-300# to make and keep a fire going, the entire firebed must be composed of only coal and at least 6-8" deep. This amount of coal in the firebed makes the redesigned OWB impractical unless you are near the coal mines and breakers.
It would be cheaper to get a used EFM, AHS, AxemanAnderson, Keystoker Harman, Van Wert or Gentlman Janitor bliler and build a building around it, to burn anthracite well. These boilers are designed to burn anthracite and the heat exchangers are designed to get the heat out of the coal exhaust, and to be cleanable to remove flyash.
Post a photo of your firebox in your OWB, if you are lucky and have one with built in grates and an ashdrawer, you could possibly make it work.
Hope this helps. Greg L