Meyer Lansky ate there, says this NYT letter by J. Sternstein. He wasn't alone:

Edward G. Robinson was also an admirer of Sussman-Volk's sandwiches. He used to dine there whenever he visited New York, and an autographed photo of him occupied an honored place behind the counter. Whether Robinson ever met Lansky over a platter of tongue and pastrami I do not know, but perhaps he did and picked up a few tips for his portrayals of Rico in "Little Caesar" and other notable celluloid mobsters.

Some say Sussman Volk 's founder was the first add put pastrami to rye bread.

What, this had never occured to anyone before?