I've cured and smoked a few corned beefs turning them into pastrami.
If you all ready have a corned beef flat from a grocery store and want to smoke it to make pastrami, I would suggest soaking the corned beef for a couple of days and changing the water at least twice a day. This helps remove salt from the curing process. I would suggest cooking a pork butt above the corned beef so that you can keep the meat moist. I would use a 4/1 ratio of cracked black pepper to cracked coriander for a rub. Adding some garlic powder and a little cayenne pepper for bite is also good.
Corned beefs smoke faster than a brisket will. You really only need to go to a temp of 160.
If you want to start from scratch with a full packer cut brisket there are several recipes of the web. I also have one I could send off the forum. The author gives some fairly detailed instructions.