Change heads (or faces) with plastic Mantic ghouls or zombies.
The changing faces give you the advantage to keep the original helmet or cap of your historical figs.

Or cut off the nose of your historical figurines and drill 2 holes for the nostril. Drill too the eyes to give them a more living dead look.
swap some hand or arms with dead ones from the same mantic and you get cheap military zombies for your era of play.

Then paint them with zombies flesh.

Eric