I realize I may have missed other related posts, but I thought I would jump in here anyway.
Even if you need to gain weight, it is not a great idea to increase your fat intake too much. Fat (especially animal fat) stores toxicity in your body and when you increase fat, you increase liklihood of a weakened immune system and getting sick more often (colds, flu, etc...)
To gain weight focus in calorie dense foods that are high in carbs and protein. Your goal is to increase muscle mass, not body fat.
Pork roast isn't bad if it is pork LOIN roast (like a center cut - lots of white meat with less fat) but you really should avoid the fattier cuts. Also avoid low-quality fatty cuts of beef, bacon, sausage, and deli meats.
Better yet, for quality protein eat lots of fish, poultry, beans, and eggs.