:P

Protien alone won't make you gain weight... You need to have more calories going into you're system than are going out. Protien contains about 4 calories per gram but you're body doesn't use much of it unless its in starvation mode.

Eat a lot of clean complex and simple carbs... Pasta, Wholegrain cereals, oats, bananas, Raisins.

Make sure you give you're body enough time to recover. you don't need to hit the weights to put on mass for boxing, I'm sure it helps but if you're just wanting to move up a weight and be able to hit hard at it change the way you do you're bag work, be explosive in you're movements, go as hard and as fast as you can, really use you're legs and shoulders.

You're legs should be where you try and put the weight on but there aren't really any weight lifting you can do to you're legs which is going to keep you're legs loose and limber. Add hill and stair sprints into you're road work.

You'll get dense, strong legs in no time. It may be worth a program geared at bulking you're upper body up but in my opinion if you'e worked you're legs properly what you already do should be enough for the upper body, as long as you work the legs and make you're bag work explosive. I don't know the exact science but if you're legs don't grow, you're arms can't grow past a certain point.

Other wise you'd end up like an upside down triangle and you're balance and anchoring would be awfull... when you're walking around... lets forget about throwing punches for a second... it'd be like punching whilst hanging from a rope