8 inb's...what's your daily caloric intake, you really trying to get to 300?
Biggest I was able to get to was 239lbs and that was after getting sober and weighing 135lbs. Took me 15mnths of eating mainly shitty carbs. I had to lose weight on purpose cause my legs were killing me going up the stairs lol...good luck if you do get there or close to it.
The trick to get to 300 pounds is to up your calories and carbs one trick I discovered from my previous bulking days is you can teach the body to eat more, every week you add a bit more food to your meals and watch the weight go up, try to get most of your calories from clean healthy foods, virgin coconut oil, peanut butter, avocados, nuts, potatoes, steak etc,
And once weekly I will get a high calories cheat meal, large pizza, huge burger etc.
Make sure to do cardio it helps when you are bulking.