Gaining

That begs the question, just how much can the body process safely? esp, fats

Everyone's different. Those weight gain calculators really don't work very well. Even if you can eat that much it doesn't mean you can digest that much.

I have seen gifted stuffers exceed two lbs a day. Like someone said it's difficult to predict what will happen. But to answer your question it is possible for some people.

That's a lot of math, and it assumes all calories are the same, and you can calculate how fast your body burns them.

I may have gained 14 lbs in a week at some point, but it's certainly not sustainable... I think you would be better at concentrating on increasing your stomach capacity so that you can eat more, and you'll feel hungrier more quickly.

There's no way to gain that amount of solid weight in a week. Maybe in water weight, or if you were to stuff enough food all at once, but I don't think it would be possible to gain 14 lbs of permanent weight.

2 Lbs a day is definitely possible. Really need to work on it though. A pound a day is quite easy to obtain.
A diet change is required of course. Anything that is high carbs should be your dietary mainstay.
Anything that is calorie dense is your friend. The name of the game is quality and quanity.
Be more of a grazer rather than a stuffer your body
needs time to adapt to your new diet.
Don't forget liquid caloric intake. Any high calorie drinks will greatly enhance your weigh gain.
Would you rather gain 2 Lbs a day or average A Lb. a day ? Remember a Lb. a day equals 30 Lbs. a month.
Also keep in mind as you grow larger your body will require more calories a day just for body maintaince.
Oink Oink