I've never cured a lean cut of meat that thin; other than pork chops. And those I've only cured for a few hours to impart a "cure" flavor, then I would pan fry them.
Four days seems a bit too long. You may have to experiment. I feel two days may be enough, or you may want to go three. Since pastrami is fully cooked anyway, and if you smoke/cook it at 200°F or higher, the end product will be safe; if the cure hadn't fully penetrated you may see an unappetizing brownish center.