got a few questions

I got the bed off a buddy of mine's 98 s-10 today, and I have a question, if I buy the notch kit, do I have to narrow the top of the frame in the rear for the notch to sit strait, it doesnt look like it would fit right, also, how do you all relocate everything, there is the gas thing over where the axle is, what do most people do with that. Also, what is the point of the gas tank crossmember, to raise the tank, or just rais the crossmember for the driveshaft?