i dont think there is much for beef shops in New Beford but i know there is some in East Boston.
http://www.yelp.com/biz/royal-roast-beef-and-seafood-bostonbut if you want to go for a little bit of a drive the BEST roast beef in New England is either going to be Billy's Roast Beef in Wakefield, MA (Disclaimer: I worked there) or Nick's Roast Beef in Beverly, MA.
Nick's is really one of the original beef shops. a good 90% of the shops in MA were started by employees of Nick's.
Next time you're up in MA try to stop in.
you can get the beef any way you want too. some people like just cheese and sauce, others cheese and mustard or just cheese and mayo.
you can get the beef rare (they slice from the thick part of the beef)
you can get it well done (a. from the skinny part of the beef that cooks faster or b. they can also throw it on the grill for a bit. throwing it on the grill creates a whole different flavor.)