Lisa, half your work is already done since you bought a brisket that is already corned!!!!! from there it's just a rub and smoke session.....dejaydebi has a version and I use a different one, mine however is based on corning my own brisket or whatnot......if you want to follow what I do then this is the link, randy seems to know his stuff!!!
It's easy! Just trim some of the excess fat off, put a nice thick layer of spices on it wrap it in plastic wrap real tight and let it site a day or two or three then smoke it like you would a brisket for slicing.
I love pastrami! 9 of of 10 of the briskets I buy become pastrami. I make New York Deli style (Italian pastrami) which is also called Kosher style in New York. NYC has some of the best pastrami in the world according to some of the fod crtiics and I agree!