Traditional pastrami (ie. Katz) is made from beef navel. I have not been able to source beef navel at a reasonable price, so I've experimented with several cuts. Many use brisket, but I find the flat too lean. The point is good, but I don't know where to get just points. I've tried chuck, but the grocery store chuck roasts have the grain going the wrong way. I've settled on boneless chuck short ribs.

Here's a typical boneless chuck short rib from a local ethnic super market. (These can also be cut from the chuck eye portion of the chuck roll)
The Recipe that I use is here:

A couple of notes
1. I go light on salt (doctor's orders)
2. Most would a LOT more pepper in the rub, but my family are not fans of a lot of pepper.
I trimmed the silver skin and the gristle where the bones were attached, here are the 3 ribs:

After curing with salt and cure#1 only (11 days), they were rinsed, patted dry, slathered with yellow mustard and applied the rub:

Then refrigerated uncovered for 3 days and smoked at 225ºF - 250ºF until a nice bark formed (internal temperature was about 150ºF:

After smoking, the meat was returned to the vacuum bags and sous vide "poached" at 135ºF for 3 days.

Then it was seared on the gas grill to harden the bark:

And sliced, meat was fall apart tender and still nice and moist:

