Jason,
I've not been to Baltimore, but I've made Baltimore Pit Beef a few times and quite enjoyed the crusty on the outside, rare on the inside goodness. I got the following loose recipe from a Baltimore native, and fellow BBQ enthusiast, a few years ago on a BBQ listsev.
Basics are a top round roast rubbed with seasoned salt (Lawry's), sweet paprika, garlic powder, dried oregano and black pepper.
Grill, rotating frequently, over a hot lump charcoal fire, the meat should be black, crusty and charred on the outside, rare on the inside. Though with a somewhat tough cut such as top round you do not want dead rare or you will not be able to chew the meat. Take the meat off the fire at 130° and let rest for 5-10 minutes.
Slice the meat very thin and serve on Kaiser rolls with sweet onion and horseradish sauce. Tomato and onion optional.
You can use prepared horseradish sauce or, it's simple to make your own. 2-parts mayonnaise (Hellmann's) to 1-part horseradish. Little lemon juice, S&P, whisk.
Load up the sandwich with thin sliced beef, white onion and horseradish sauce, eat, drip horseradish sauce on your shirt.
Enjoy,
Gary