Use the Ruhlman/Polcyn recipe to make corned beef, then soak the Pastrami in fresh water overnight to desalinate.
Spice rub:
- 1 Tbsp Black peppercorns
- 1 Tbsp Coriander seeds
- 1 tsp Garlic
- 1 Tbsp Paprika
- 1 tsp Onion
- 1 tsp Mustard seed
Apply it with some yellow mustard to get it to stick, then smoke at 225F until it reaches ~160F and has a brown crust. Do the Texas Crutch (wrap in foil and heat until 203F). Cherry wood. I like to use a foil pan so it is easier to move and cover.
Reheat covered in the oven with a bit of water for steam.
Sources:

A Homemade Smoked Pastrami Recipe That’s Close To Katz’s
If you’ve ever wondered how to make pastrami then we’ve got you covered. Moist, tender, and full of flavor, this is the ultimate homemade smoked pastrami recipe. So what is pastrami? Simply put, it’s Jewish barbecue, i.e. corned beef that has been smoked. This is about as close to Katz’s pastrami recipe as you’ll get!

The Pastrami Rub Recipe That Puts Famous Katz’s Deli On Notice
Pastrami depends heavily on the spice blend applied to the cured corned beef. But the distinctive combination of coriander, black pepper, and other spices works wonders on goose or duck breast, on pork belly, on beef short ribs to name a few options. After much research and trial and error, here’s my approximation of Katz’s pastrami rub recipe.