chances are that the bottom of the tank is probably less rusty then the top area, do to the fact that when you store it there is usually some fuel left covering the lower area of the tank. the condensate usually collects above the level of the fuel and rusts the upper area,rust likes water and air to "grow". you should be able to tap along the questionable area and hear a distinct difference in sound, along the lines of a tin can sound, if the metal has become real thin. try tapping it gently with the butt of a screw driver or something along the seam, it should have a fairly dense sound to it. if you are still leary of the acid, you can do the old school gravel thing..... rinse the tank out completely! let it air out all the gas fumes! fill the tank about halfway with water and a couple handfulls of small gravel, and shake shake shake. its like sanding the inside, it will knock of the stuff that is on the surface (the stuff most likely to break free as you ride and clog your filter). then rinse it all out, and get it good and dry inside. then you will have a clean enough surface for the kreem to work. i have done this a few times long ago in the metal tank days, before plastic tanks came along.
as far as the drum it should slide off the axle once the cover and stuff are out of the way, its probably rusted to the splines on the axle. try some penetrating spray or wd40 let it sit for a bit the tap around the spline area on the drum..not on the outer drum!! lol just by the axle area! tap it a few times and it should break free and slide off, after that the shoes are a breeze.