oversized

I'm thinking about getting a 84mm weisco piston for my 1998 yamaha warrior 350 will it fit and if so will it make faster or stronger or hopefully both

I was wondering if I should get a 3.4 gallon gas tank for my 98 warrior they are expensive so I don't want to make a bad decision so I was asking you're guys you're opinion and if so I was wondering if someone could show me how to install it